diff --git a/CLAUDE.md b/CLAUDE.md
index 63ebcc6..a24d824 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -41,6 +41,7 @@ cargo test -- --ignored                     # 会读写真实钥匙串的测试
 - `session/` — `model.rs`（Session / SessionGroup / SessionDraft / GroupDraft / `HostOs`；`Session.group` 与 `SessionGroup.parent` 都是 `Option<GroupId>`，`Session.os` 是 `Option<HostOs>`）、`database.rs`（`SessionDatabase`：rusqlite 连接、`PRAGMA user_version` 迁移、行与模型的映射）、`store.rs`（`SessionStore` 实体，**内存是唯一事实来源**，写穿到数据库）、`outline.rs`（纯函数：store → `TreeItem`，递归铺开嵌套分组；节点 id 形如 `g:<id>` / `s:<id>`；`group_options` 给表单提供按全路径标注的分组列表）、`session_panel.rs`（左侧 Dock 面板：搜索 + 树 + 右键菜单）、`session_dialog.rs`、`group_dialog.rs`（`GroupForm`、`open_group_dialog`、`confirm_delete_group`）。
 - `terminal/` — 本地终端是真的：`transport.rs`（字节流传输的 trait）、`local_pty.rs`（`portable-pty` 实现，跑在专用线程上）、`engine.rs`（驱动 `alacritty_terminal`，解析线程 + 16ms UI 轮询批量刷新）、`terminal_view.rs`（网格渲染、选区、输入编码）、`local_terminal_panel.rs`（⌘T 开的本地标签页）、`model.rs`。远程会话的传输在 `ssh/`，中间区的标签页是 `terminal_panel.rs`。共享 prompt 协议位于 `connection.rs`，`transport.rs` 通过 `TerminalPrompt` / `TerminalPromptKind` / `TerminalSecret` 重导出保持兼容。
 - `ssh/` — `probe.rs`（探测远端系统的命令与纯解析函数，外加驱动两步探测的 `HostOsProbe` 状态机）、`transport.rs`：真实的 russh 客户端。known_hosts 校验写 `<data_dir>/known_hosts`（**不碰** `~/.ssh/known_hosts`），认证链是 agent → publickey → password → keyboard-interactive。密码和私钥口令先查 `secrets`，查不到或被服务器拒绝才走 prompt 弹框；被拒绝时**不删**钥匙串条目，只在弹框说明里讲清原因。shell 起来后主循环每 5 秒用 `Handle::send_ping()`（`keepalive@openssh.com`，服务器回成功或失败都算回复）量一次往返，5 秒没回就记为超时，结果以 `TerminalTransportEvent::Latency` 送出；引擎把最新一次存成状态（和 `lifecycle` 一样，重启、退出、失败时清空），`TerminalPanel::title_suffix` 在标签栏右侧显示：< 100 ms 用 `success`，100–200 ms 用 `warning`，> 200 ms 或超时用 `danger`，分档在 `Latency::level`。
+- **会话对话框的「测试连接」是真登录。** 会话模块不依赖 `ssh`：`connection.rs` 定义 `LoginTest`（表单当前值，秘密用 `Zeroizing`，`Debug` 打码）和 `ConnectionTester` 接口，工作区用和终端 / SFTP 共享的 `SshConnector` 造 `ssh::SshConnectionTester` 注入进去（`Workspace::new_with_services` 的最后一个服务参数，UI 测试注入 `FakeConnectionTester`）。测试用的秘密来源 `FormSecrets` 只读：本端点的登录密码、表单所选私钥的口令只认表单里的值（钥匙串里的旧密码不参与），其余条目回退钥匙串，从不写入。`SshPrompts::non_interactive()` 让缺密码 / 口令 / 键盘交互直接以带类型的 `MissingCredential` 失败而不弹框，失败原因由 `tester.rs` 的 `describe_test_failure` 按类型映射成中文。陌生主机密钥仍然要问：工作线程通过 channel 把问题交给表单，表单每 50 ms 轮询，在会话对话框上方弹「首次连接此主机」，信任就写入 known_hosts；密钥已变化一律判失败。结果只以通知呈现：「连接成功」，或标题「连接失败」加原因。
 - `secrets/` — 系统钥匙串（`keyring` 4：macOS Keychain / Windows 凭据管理器 / Secret Service）。`SecretRef` 决定归属：密码按 `user@host:port`（改名、复制会话都不丢，同一台机器的多个会话共用一条），私钥口令按文件路径（同一把钥匙只问一次）。`SecretStore` 的三个方法全是阻塞的，**只能**在后台执行器或传输层工作线程上调用。`InMemorySecretStore` 给测试，`NoSecretStore` 给没有钥匙串的机器（界面据此禁用密码字段）。
 - `explorer/` — 目录与选择快照、`DataTable` 双栏、上传确认 / 冲突对话框、进度和取消 / 恢复展示。`ExplorerAction` 统一路由到工作区；文件扫描与网络操作在后台，目录响应按请求编号丢弃过期结果。
 - `sftp/` — 可注入传输与本地目录接口、`RemotePath`、russh-sftp 3.0.0 协议适配、有界并发分块上传、UUID 临时文件、安全替换、原子 JSON 续传记录和三次自动重连。`ssh/connection.rs` 的 `SshConnector` 与终端共享认证、钥匙串服务及 known_hosts 写锁。
@@ -72,4 +73,4 @@ cargo test -- --ignored                     # 会读写真实钥匙串的测试
 
 ## 测试约定
 
-UI 测试（`tests/ui.rs`）在无头窗口里渲染真实的 `Workspace`，通过 `gpui_kit::test::TestWindowExt`（`click`、`double_click`、`input`、`press`、`find`、`within`）驱动。`Workspace::new` 要求外部传入 `Entity<SessionStore>`：生产环境由 `main.rs` 从数据库加载，测试用 `open_workspace_with_store` 注入 `SessionStore::seed()`（或一个临时文件上的真库）。**不要用右键菜单驱动测试**：菜单项的 ElementId 只是序号，而且 `PopupMenu` 实体会让测试以「leaked handles」失败；直接 `window.dispatch_action` 派发菜单会派发的那个动作。测试模块里要显式导入类型，`use gpui_kit::*` 会遮蔽 `#[test]`。被测试查询的元素带稳定的领域 id，自定义 `div` 还要加 `.test_support()`：`("session-row", id)`、`("session-os", id)` 与开始页的 `("recent-session-os", id)`（`aria_label` 是系统名，未探测时是「未探测到系统」）、`("group-row", id)`、`("terminal", id)`、`("explorer", id)`、`("local-pane"|"remote-pane", id)`、`("close-terminal", id)`、`("close-explorer", id)`、标签标题 `("terminal-tab", id)` / `("explorer-tab", session_id)` / `("local-terminal-tab", id)`（`aria_label` 是标签文字）、`("terminal-tab-os", id)`、`("terminal-latency", id)`（`aria_label` 是「32 ms」或「超时」）、`tab-name`（重命名标签对话框）、`recent-sessions`、`("recent-session", id)`、`recent-new-session`、`session-search`、`new-session`、`new-group`、`theme-toggle`、`status-connection`、`commit`、`ok`（确认对话框）、`form-error`、`session-name` / `-host` / `-port` / `-user` / `-auth` / `-key-path` / `-password` / `-passphrase`、`group-name`、`remote-path`。被遮蔽的输入框在测试里读不到值（`ElementSnapshot::value()` 返回 `None`），所以密码相关的断言一律查注入的 `InMemorySecretStore`，不查界面。动作派发和 `set_active` 都是延迟执行的：先退出 `update_window`，调用 `cx.run_until_parked()`，再 `render_frame` 后断言。种子会话 id 按插入顺序（`web-01`=1 … `dev-box`=6），种子分组同理（`生产`=1、`测试`=2、`开发`=3）；`web-01` 与 `staging-api` 初始为已连接并已打开终端标签。
+UI 测试（`tests/ui.rs`）在无头窗口里渲染真实的 `Workspace`，通过 `gpui_kit::test::TestWindowExt`（`click`、`double_click`、`input`、`press`、`find`、`within`）驱动。`Workspace::new` 要求外部传入 `Entity<SessionStore>`：生产环境由 `main.rs` 从数据库加载，测试用 `open_workspace_with_store` 注入 `SessionStore::seed()`（或一个临时文件上的真库）。**不要用右键菜单驱动测试**：菜单项的 ElementId 只是序号，而且 `PopupMenu` 实体会让测试以「leaked handles」失败；直接 `window.dispatch_action` 派发菜单会派发的那个动作。测试模块里要显式导入类型，`use gpui_kit::*` 会遮蔽 `#[test]`。被测试查询的元素带稳定的领域 id，自定义 `div` 还要加 `.test_support()`：`("session-row", id)`、`("session-os", id)` 与开始页的 `("recent-session-os", id)`（`aria_label` 是系统名，未探测时是「未探测到系统」）、`("group-row", id)`、`("terminal", id)`、`("explorer", id)`、`("local-pane"|"remote-pane", id)`、`("close-terminal", id)`、`("close-explorer", id)`、标签标题 `("terminal-tab", id)` / `("explorer-tab", session_id)` / `("local-terminal-tab", id)`（`aria_label` 是标签文字）、`("terminal-tab-os", id)`、`test-connection`、`("terminal-latency", id)`（`aria_label` 是「32 ms」或「超时」）、`tab-name`（重命名标签对话框）、`recent-sessions`、`("recent-session", id)`、`recent-new-session`、`session-search`、`new-session`、`new-group`、`theme-toggle`、`status-connection`、`commit`、`ok`（确认对话框）、`form-error`、`session-name` / `-host` / `-port` / `-user` / `-auth` / `-key-path` / `-password` / `-passphrase`、`group-name`、`remote-path`。被遮蔽的输入框在测试里读不到值（`ElementSnapshot::value()` 返回 `None`），所以密码相关的断言一律查注入的 `InMemorySecretStore`，不查界面。动作派发和 `set_active` 都是延迟执行的：先退出 `update_window`，调用 `cx.run_until_parked()`，再 `render_frame` 后断言。种子会话 id 按插入顺序（`web-01`=1 … `dev-box`=6），种子分组同理（`生产`=1、`测试`=2、`开发`=3）；`web-01` 与 `staging-api` 初始为已连接并已打开终端标签。
diff --git a/src/connection.rs b/src/connection.rs
index 7fab5cd..236dc59 100644
--- a/src/connection.rs
+++ b/src/connection.rs
@@ -73,6 +73,14 @@ impl UnknownHostPrompt {
     pub fn fingerprint(&self) -> &str {
         &self.fingerprint
     }
+
+    /// What the trust dialog tells the user about the key.
+    pub fn description(&self) -> String {
+        format!(
+            "主机：{}:{}\n算法：{}\nSHA-256 指纹：{}\n\n请先确认该指纹来自可信渠道。",
+            self.host, self.port, self.algorithm, self.fingerprint,
+        )
+    }
 }
 
 #[derive(Clone, Debug, PartialEq, Eq)]
@@ -212,3 +220,102 @@ impl std::fmt::Debug for ConnectionPromptReply {
         }
     }
 }
+
+/// What a connection test logs in with: the session form's current values,
+/// saved or not. Secrets stay zeroized and never print.
+pub struct LoginTest {
+    host: String,
+    port: u16,
+    user: String,
+    auth: crate::session::AuthKind,
+    key_path: Option<std::path::PathBuf>,
+    password: Option<Zeroizing<String>>,
+    passphrase: Option<Zeroizing<String>>,
+}
+
+impl LoginTest {
+    pub fn new(
+        host: impl Into<String>,
+        port: u16,
+        user: impl Into<String>,
+        auth: crate::session::AuthKind,
+    ) -> Self {
+        Self {
+            host: host.into(),
+            port,
+            user: user.into(),
+            auth,
+            key_path: None,
+            password: None,
+            passphrase: None,
+        }
+    }
+
+    pub fn with_key_path(mut self, path: impl Into<std::path::PathBuf>) -> Self {
+        self.key_path = Some(path.into());
+        self
+    }
+
+    pub fn with_password(mut self, password: impl Into<String>) -> Self {
+        self.password = Some(Zeroizing::new(password.into()));
+        self
+    }
+
+    pub fn with_passphrase(mut self, passphrase: impl Into<String>) -> Self {
+        self.passphrase = Some(Zeroizing::new(passphrase.into()));
+        self
+    }
+
+    pub fn host(&self) -> &str {
+        &self.host
+    }
+    pub fn port(&self) -> u16 {
+        self.port
+    }
+    pub fn user(&self) -> &str {
+        &self.user
+    }
+    pub fn auth(&self) -> crate::session::AuthKind {
+        self.auth
+    }
+    pub fn key_path(&self) -> Option<&std::path::Path> {
+        self.key_path.as_deref()
+    }
+    pub fn password(&self) -> Option<&str> {
+        self.password.as_deref().map(String::as_str)
+    }
+    pub fn passphrase(&self) -> Option<&str> {
+        self.passphrase.as_deref().map(String::as_str)
+    }
+}
+
+impl std::fmt::Debug for LoginTest {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("LoginTest")
+            .field("host", &self.host)
+            .field("port", &self.port)
+            .field("user", &self.user)
+            .field("auth", &self.auth)
+            .field("key_path", &self.key_path)
+            .field("password", &self.password.as_ref().map(|_| "<redacted>"))
+            .field(
+                "passphrase",
+                &self.passphrase.as_ref().map(|_| "<redacted>"),
+            )
+            .finish()
+    }
+}
+
+/// Answers whether to trust a host key seen for the first time. It blocks
+/// until a person decides; `false` also covers "nobody is there to ask".
+pub type TrustCallback = Box<dyn Fn(UnknownHostPrompt) -> bool + Send + Sync>;
+
+/// Logs in once with a [`LoginTest`] and hangs up, so the session form can
+/// check its values before saving them.
+pub trait ConnectionTester: Send + Sync + 'static {
+    /// Blocks: call it on a thread of its own. `Err` holds the reason, worded
+    /// for the user.
+    fn test(&self, request: LoginTest, trust: TrustCallback) -> Result<(), String>;
+}
+
+pub type SharedConnectionTester = std::sync::Arc<dyn ConnectionTester>;
diff --git a/src/session/session_dialog.rs b/src/session/session_dialog.rs
index d1b3525..e7f58a3 100644
--- a/src/session/session_dialog.rs
+++ b/src/session/session_dialog.rs
@@ -7,14 +7,15 @@ use gpui_kit::component::{
     form::{Field, Form},
     h_flex,
     input::{Input, InputContentType, InputEvent, InputState},
+    notification::Notification,
     select::{Select, SelectState},
     v_flex,
 };
 use gpui_kit::prelude::FluentBuilder as _;
 use gpui_kit::*;
-use tokio::io::{AsyncReadExt as _, AsyncWriteExt as _};
 use zeroize::Zeroizing;
 
+use crate::connection::{LoginTest, SharedConnectionTester, TrustCallback, UnknownHostPrompt};
 use crate::secrets::{SecretRef, SharedSecretStore};
 
 use super::{AuthKind, GroupId, Session, SessionDraft, SessionId, SessionStore, group_options};
@@ -53,7 +54,8 @@ pub struct SessionForm {
     group_ids: Vec<Option<GroupId>>,
     error: Option<SharedString>,
     testing_connection: bool,
-    connection_test_result: Option<(bool, SharedString)>,
+    /// Logs in with the form's current values for 「测试连接」.
+    tester: SharedConnectionTester,
     editing_connected: bool,
     /// Where saved secrets are read from. Writes go through the store, which
     /// owns the one error channel.
@@ -72,6 +74,7 @@ impl SessionForm {
         editing: Option<SessionId>,
         preselect_group: Option<GroupId>,
         store: Entity<SessionStore>,
+        tester: SharedConnectionTester,
         window: &mut Window,
         cx: &mut Context<Self>,
     ) -> Self {
@@ -183,7 +186,7 @@ impl SessionForm {
             group_ids,
             error: None,
             testing_connection: false,
-            connection_test_result: None,
+            tester,
             editing_connected,
             secrets,
             password_loaded: false,
@@ -283,47 +286,118 @@ impl SessionForm {
         .detach();
     }
 
-    /// Probe the endpoint currently shown in the form without saving it.
-    fn test_connection(&mut self, _: &ClickEvent, _: &mut Window, cx: &mut Context<Self>) {
+    /// The login the form's current values describe, saved or not, or why
+    /// there is nothing to test yet.
+    fn login_test(&self, cx: &App) -> Result<LoginTest, &'static str> {
+        let host = self.host.read(cx).value().trim().to_string();
+        let port = parse_port(self.port.read(cx).value().trim());
+        let user = self.user.read(cx).value().trim().to_string();
+        let auth = self
+            .auth
+            .read(cx)
+            .selected_index(cx)
+            .and_then(|ix| AuthKind::ALL.get(ix.row).copied())
+            .unwrap_or_default();
+        let key_path = self.key_path.read(cx).value().trim().to_string();
+        let port = match (host.is_empty(), port, user.is_empty()) {
+            (true, _, _) => return Err("请输入主机"),
+            (_, None, _) => return Err("端口必须是 1 到 65535 之间的数字"),
+            (_, _, true) => return Err("请输入用户名"),
+            (_, Some(port), _) => port,
+        };
+        if auth == AuthKind::Key && key_path.is_empty() {
+            return Err("私钥认证需要选择私钥文件");
+        }
+        let mut request = LoginTest::new(host, port, user, auth);
+        // Only what the chosen method uses, which is also what the form shows.
+        if uses_password(auth) {
+            let password = self.password.read(cx).value();
+            if !password.is_empty() {
+                request = request.with_password(password.to_string());
+            }
+        }
+        if auth == AuthKind::Key {
+            request = request.with_key_path(key_path);
+            let passphrase = self.passphrase.read(cx).value();
+            if !passphrase.is_empty() {
+                request = request.with_passphrase(passphrase.to_string());
+            }
+        }
+        Ok(request)
+    }
+
+    /// Log in with the form's current values without saving them, and report
+    /// the outcome as a notification. The login runs on a thread of its own;
+    /// a host key seen for the first time is put to the user in a dialog
+    /// above this one.
+    fn test_connection(&mut self, _: &ClickEvent, window: &mut Window, cx: &mut Context<Self>) {
         if self.testing_connection {
             return;
         }
-        let host = self.host.read(cx).value().trim().to_string();
-        let port = self.port.read(cx).value().trim().parse::<u16>();
-        let error = if host.is_empty() {
-            Some("请输入主机")
-        } else if !matches!(port, Ok(1..=u16::MAX)) {
-            Some("端口必须是 1 到 65535 之间的数字")
-        } else {
-            None
+        let request = match self.login_test(cx) {
+            Ok(request) => request,
+            Err(reason) => {
+                window.push_notification(connection_test_notification(Err(reason.into())), cx);
+                return;
+            }
         };
-        if let Some(error) = error {
-            self.connection_test_result = Some((false, error.into()));
-            cx.notify();
+        let (trust_tx, trust_rx) = std::sync::mpsc::channel::<TrustQuestion>();
+        let (result_tx, result_rx) = std::sync::mpsc::channel();
+        let tester = self.tester.clone();
+        let spawned = std::thread::Builder::new()
+            .name("shellr-connection-test".into())
+            .spawn(move || {
+                // Nobody left to answer (the form closed) reads as "no".
+                let trust: TrustCallback = Box::new(move |prompt| {
+                    let (reply_tx, reply_rx) = std::sync::mpsc::channel();
+                    trust_tx.send((prompt, reply_tx)).is_ok() && reply_rx.recv().unwrap_or(false)
+                });
+                let _ = result_tx.send(tester.test(request, trust));
+            });
+        if let Err(error) = spawned {
+            window.push_notification(
+                connection_test_notification(Err(format!("无法启动连接测试：{error}"))),
+                cx,
+            );
             return;
         }
-        let port = port.expect("validated port");
-        let endpoint = format!("{host}:{port}");
         self.testing_connection = true;
-        self.connection_test_result = None;
         cx.notify();
-        cx.spawn(async move |this, cx| {
-            let result = cx
-                .background_executor()
-                .spawn(async move { probe_ssh_service(&host, port) })
-                .await;
-            this.update_in(cx, |this, _, cx| {
-                this.testing_connection = false;
-                this.connection_test_result = Some(match result {
-                    Ok(()) => (
-                        true,
-                        format!("{endpoint}：SSH 服务可达，尚未验证登录认证").into(),
-                    ),
-                    Err(error) => (false, format!("{endpoint}：{error}").into()),
-                });
-                cx.notify();
-            })
-            .ok();
+        // Polled rather than woken by the worker, as with every other worker
+        // in the application.
+        cx.spawn_in(window, async move |this, cx| {
+            loop {
+                cx.background_executor()
+                    .timer(Duration::from_millis(50))
+                    .await;
+                while let Ok((prompt, reply)) = trust_rx.try_recv() {
+                    if this
+                        .update_in(cx, |_, window, cx| ask_to_trust(prompt, reply, window, cx))
+                        .is_err()
+                    {
+                        return;
+                    }
+                }
+                let result = match result_rx.try_recv() {
+                    Ok(result) => result,
+                    Err(std::sync::mpsc::TryRecvError::Empty) => {
+                        if this.update(cx, |_, _| ()).is_err() {
+                            return;
+                        }
+                        continue;
+                    }
+                    Err(std::sync::mpsc::TryRecvError::Disconnected) => {
+                        Err("连接测试意外中止".to_string())
+                    }
+                };
+                this.update_in(cx, |this, window, cx| {
+                    this.testing_connection = false;
+                    window.push_notification(connection_test_notification(result), cx);
+                    cx.notify();
+                })
+                .ok();
+                return;
+            }
         })
         .detach();
     }
@@ -555,70 +629,64 @@ impl Render for SessionForm {
                         .child(error),
                 )
             })
-            .when_some(
-                self.connection_test_result.clone(),
-                |form, (success, message)| {
-                    form.child(
-                        div()
-                            .id("connection-test-result")
-                            .test_support()
-                            .aria_label(message.clone())
-                            .text_sm()
-                            .text_color(if success {
-                                cx.theme().success
-                            } else {
-                                cx.theme().danger
-                            })
-                            .child(message),
-                    )
-                },
-            )
     }
 }
 
-/// Check that a TCP endpoint speaks SSH. Authentication is intentionally not
-/// attempted, so the form can test unsaved hosts without storing credentials
-/// or changing the application's trusted-host list.
-fn probe_ssh_service(host: &str, port: u16) -> Result<(), String> {
-    let runtime = tokio::runtime::Builder::new_current_thread()
-        .enable_all()
-        .build()
-        .map_err(|error| format!("无法启动连接测试：{error}"))?;
-    runtime.block_on(async {
-        tokio::time::timeout(Duration::from_secs(8), async {
-            let mut stream = tokio::net::TcpStream::connect((host, port))
-                .await
-                .map_err(|error| format!("无法连接：{error}"))?;
-            stream
-                .write_all(b"SSH-2.0-shellr-probe\r\n")
-                .await
-                .map_err(|error| format!("无法发送 SSH 标识：{error}"))?;
-            for _ in 0..10 {
-                let mut line = Vec::new();
-                for _ in 0..255 {
-                    let byte = stream
-                        .read_u8()
-                        .await
-                        .map_err(|error| format!("无法读取 SSH 标识：{error}"))?;
-                    if byte == b'\n' {
-                        break;
-                    }
-                    line.push(byte);
-                }
-                if line.starts_with(b"SSH-2.0-") || line.starts_with(b"SSH-1.99-") {
-                    return Ok(());
-                }
-            }
-            Err("目标端口没有返回 SSH 服务标识".to_string())
-        })
-        .await
-        .map_err(|_| "连接超时".to_string())?
-    })
+/// A trust question from the test's worker, with where to send the answer.
+type TrustQuestion = (UnknownHostPrompt, std::sync::mpsc::Sender<bool>);
+
+/// A port field's value, when it is one.
+fn parse_port(port: &str) -> Option<u16> {
+    port.parse::<u16>().ok().filter(|port| *port != 0)
+}
+
+/// Put a first-seen host key to the user, above the session dialog. Closing
+/// the dialog any other way than trusting counts as declining.
+fn ask_to_trust(
+    prompt: UnknownHostPrompt,
+    reply: std::sync::mpsc::Sender<bool>,
+    window: &mut Window,
+    cx: &mut App,
+) {
+    let description = prompt.description();
+    window.open_alert_dialog(cx, move |alert, _, _| {
+        let answer = |trusted: bool| {
+            let reply = reply.clone();
+            move || {
+                let _ = reply.send(trusted);
+            }
+        };
+        let (trust, decline, dismiss) = (answer(true), answer(false), answer(false));
+        alert
+            .title("首次连接此主机")
+            .description(description.clone())
+            .button_props(
+                DialogButtonProps::default()
+                    .ok_text("信任并继续")
+                    .cancel_text("取消"),
+            )
+            .show_cancel(true)
+            .on_ok(move |_, _, _| {
+                trust();
+                true
+            })
+            .on_cancel(move |_, _, _| {
+                decline();
+                true
+            })
+            .on_close(move |_, _, _| dismiss())
+    });
+}
+
+/// A connection test has two outcomes: it connected, or it did not and the
+/// message says why.
+fn connection_test_notification(result: Result<(), String>) -> Notification {
+    match result {
+        Ok(()) => Notification::success("连接成功"),
+        Err(reason) => Notification::error(reason).title("连接失败"),
+    }
 }
 
-/// Open the new-session (`editing == None`) or edit-session dialog.
-/// `preselect_group` fills in the group field of a new session, so creating
-/// one from a group's context menu lands it in that group.
 /// Whether this authentication kind can end up asking for a password.
 /// `Auto` walks agent, then keys, then password, so it can.
 fn uses_password(auth: AuthKind) -> bool {
@@ -641,14 +709,19 @@ fn secret_change(value: String, loaded: bool) -> Option<Option<String>> {
     }
 }
 
+/// Open the new-session (`editing == None`) or edit-session dialog.
+/// `preselect_group` fills in the group field of a new session, so creating
+/// one from a group's context menu lands it in that group. `tester` backs the
+/// dialog's 「测试连接」 button.
 pub fn open_session_dialog(
     editing: Option<SessionId>,
     preselect_group: Option<GroupId>,
     store: Entity<SessionStore>,
+    tester: SharedConnectionTester,
     window: &mut Window,
     cx: &mut App,
 ) {
-    let form = cx.new(|cx| SessionForm::new(editing, preselect_group, store, window, cx));
+    let form = cx.new(|cx| SessionForm::new(editing, preselect_group, store, tester, window, cx));
     let title: SharedString = if editing.is_some() {
         "编辑会话"
     } else {
@@ -759,7 +832,16 @@ pub fn confirm_delete_session(
 
 #[cfg(test)]
 mod tests {
-    use super::{AuthKind, secret_change, uses_password};
+    use super::{AuthKind, parse_port, secret_change, uses_password};
+
+    #[test]
+    fn a_port_field_is_a_number_from_1_to_65535() {
+        assert_eq!(parse_port("22"), Some(22));
+        assert_eq!(parse_port("65535"), Some(65535));
+        for port in ["0", "65536", "ssh", ""] {
+            assert_eq!(parse_port(port), None, "{port:?}");
+        }
+    }
 
     #[test]
     fn auto_and_password_can_reach_a_password_prompt() {
diff --git a/src/ssh/connection.rs b/src/ssh/connection.rs
index e0179da..10d8c32 100644
--- a/src/ssh/connection.rs
+++ b/src/ssh/connection.rs
@@ -78,6 +78,21 @@ impl SshConnector {
         &self,
         config: &SshConnectionConfig,
         broker: Arc<SshPrompts>,
+    ) -> Result<(client::Handle<SshClientHandler>, String)> {
+        self.connect_with(config, broker, &self.secrets).await
+    }
+
+    /// The keychain this connector reads saved secrets from.
+    pub(super) fn secrets(&self) -> &SharedSecretStore {
+        &self.secrets
+    }
+
+    /// Same as [`Self::connect`], with saved secrets read from `secrets`.
+    pub(super) async fn connect_with(
+        &self,
+        config: &SshConnectionConfig,
+        broker: Arc<SshPrompts>,
+        secrets: &SharedSecretStore,
     ) -> Result<(client::Handle<SshClientHandler>, String)> {
         let fingerprint = Arc::new(Mutex::new(String::new()));
         let handler = SshClientHandler {
@@ -104,7 +119,7 @@ impl SshConnector {
             _ = shutdown.changed() => bail!("连接已取消"),
         };
         tokio::select! {
-            result = authenticate(&mut handle, config, &self.secrets, &broker) => result?,
+            result = authenticate(&mut handle, config, secrets, &broker) => result?,
             _ = shutdown.changed() => bail!("连接已取消"),
         }
         let fingerprint = fingerprint
@@ -115,6 +130,26 @@ impl SshConnector {
     }
 }
 impl SshConnectionConfig {
+    pub fn new(
+        host: impl Into<String>,
+        port: u16,
+        user: impl Into<String>,
+        auth: AuthKind,
+        key_path: Option<PathBuf>,
+    ) -> Self {
+        Self {
+            host: host.into(),
+            port,
+            user: user.into(),
+            auth,
+            key_path,
+        }
+    }
+
+    pub fn host(&self) -> &str {
+        &self.host
+    }
+
     pub fn endpoint(&self) -> String {
         format!("{}@{}:{}", self.user, self.host, self.port)
     }
@@ -125,8 +160,41 @@ pub struct SshPrompts {
     events: Arc<dyn Fn(ConnectionPrompt) -> bool + Send + Sync>,
     shutdown: watch::Receiver<bool>,
     prompt_activity: watch::Sender<bool>,
+    /// Whether a password, passphrase or keyboard-interactive answer may be
+    /// asked of the user. When not, such a need fails the connection with a
+    /// [`MissingCredential`] instead.
+    interactive: bool,
 }
 
+/// A credential authentication needed and could not ask for, because the
+/// connection runs without anyone to answer (a connection test).
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum MissingCredential {
+    /// `rejected` when a password was tried and the server refused it.
+    Password {
+        rejected: bool,
+    },
+    /// `rejected` when a passphrase was tried and did not unlock the key.
+    Passphrase {
+        rejected: bool,
+    },
+    KeyboardInteractive,
+}
+
+impl std::fmt::Display for MissingCredential {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(match self {
+            MissingCredential::Password { rejected: true } => "用户名或密码错误",
+            MissingCredential::Password { rejected: false } => "未填写密码",
+            MissingCredential::Passphrase { rejected: true } => "私钥口令错误",
+            MissingCredential::Passphrase { rejected: false } => "私钥已加密，未填写口令",
+            MissingCredential::KeyboardInteractive => "服务器要求键盘交互式认证，无法在测试中完成",
+        })
+    }
+}
+
+impl std::error::Error for MissingCredential {}
+
 impl SshPrompts {
     pub fn new(
         events: Arc<dyn Fn(ConnectionPrompt) -> bool + Send + Sync>,
@@ -138,14 +206,21 @@ impl SshPrompts {
             events,
             shutdown,
             prompt_activity,
+            interactive: true,
         }
     }
 
+    /// Fail on a credential need instead of asking; see [`MissingCredential`].
+    pub fn non_interactive(mut self) -> Self {
+        self.interactive = false;
+        self
+    }
+
     pub fn shutdown_receiver(&self) -> watch::Receiver<bool> {
         self.shutdown.clone()
     }
 
-    fn prompt_activity_receiver(&self) -> watch::Receiver<bool> {
+    pub(super) fn prompt_activity_receiver(&self) -> watch::Receiver<bool> {
         self.prompt_activity.subscribe()
     }
 
@@ -176,6 +251,18 @@ impl SshPrompts {
         result
     }
 
+    /// Ask for a credential, or fail with `need` when nobody may be asked.
+    async fn ask_credential(
+        &self,
+        need: MissingCredential,
+        kind: ConnectionPromptKind,
+    ) -> Result<ConnectionPromptReply> {
+        if !self.interactive {
+            return Err(need.into());
+        }
+        self.ask(kind).await
+    }
+
     async fn emit(&self, kind: ConnectionPromptKind) {
         let request_id = NEXT_PROMPT_ID.fetch_add(1, Ordering::Relaxed);
         (self.events)(ConnectionPrompt::new(request_id, kind));
@@ -202,7 +289,7 @@ impl SshPrompts {
 
 /// Apply the network handshake timeout without counting time spent waiting
 /// for an explicit answer from the user to a host-trust prompt.
-async fn timeout_excluding_prompts<F>(
+pub(super) async fn timeout_excluding_prompts<F>(
     future: F,
     mut prompt_activity: watch::Receiver<bool>,
     timeout: Duration,
@@ -434,7 +521,16 @@ where
             };
             if !partial && methods.contains(&MethodKind::Password) {
                 for _ in 0..AUTH_RETRIES {
-                    let answer = ask_one_secret(broker, "SSH 登录", instructions, "密码").await?;
+                    let answer = ask_one_secret(
+                        broker,
+                        MissingCredential::Password {
+                            rejected: saved_rejected,
+                        },
+                        "SSH 登录",
+                        instructions,
+                        "密码",
+                    )
+                    .await?;
                     let result = handle
                         .authenticate_password(&config.user, answer.into_inner())
                         .await
@@ -547,7 +643,16 @@ async fn load_private_key(
         format!("请输入 {} 的口令", path.display())
     };
     for _ in 0..AUTH_RETRIES {
-        let answer = ask_one_secret(broker, "私钥口令", &instructions, "口令").await?;
+        let answer = ask_one_secret(
+            broker,
+            MissingCredential::Passphrase {
+                rejected: saved_rejected,
+            },
+            "私钥口令",
+            &instructions,
+            "口令",
+        )
+        .await?;
         if let Ok(key) = load_secret_key(path, Some(answer.expose())) {
             return Ok(Some(key));
         }
@@ -577,16 +682,20 @@ fn saved_secret(secrets: &SharedSecretStore, secret: &SecretRef) -> Option<Zeroi
 
 async fn ask_one_secret(
     broker: &SshPrompts,
+    need: MissingCredential,
     title: &str,
     instructions: &str,
     label: &str,
 ) -> Result<crate::connection::ConnectionSecret> {
     let reply = broker
-        .ask(ConnectionPromptKind::authentication(
-            title,
-            instructions,
-            vec![ConnectionPromptField::new(label, false)],
-        ))
+        .ask_credential(
+            need,
+            ConnectionPromptKind::authentication(
+                title,
+                instructions,
+                vec![ConnectionPromptField::new(label, false)],
+            ),
+        )
         .await?;
     match reply {
         ConnectionPromptReply::Answers(mut answers) if answers.len() == 1 => Ok(answers.remove(0)),
@@ -621,11 +730,10 @@ where
                     .map(|prompt| ConnectionPromptField::new(prompt.prompt, prompt.echo))
                     .collect();
                 let reply = broker
-                    .ask(ConnectionPromptKind::authentication(
-                        name,
-                        instructions,
-                        fields,
-                    ))
+                    .ask_credential(
+                        MissingCredential::KeyboardInteractive,
+                        ConnectionPromptKind::authentication(name, instructions, fields),
+                    )
                     .await?;
                 let ConnectionPromptReply::Answers(answers) = reply else {
                     bail!("交互式认证已取消")
diff --git a/src/ssh/mod.rs b/src/ssh/mod.rs
index 7f58151..e1299b0 100644
--- a/src/ssh/mod.rs
+++ b/src/ssh/mod.rs
@@ -1,6 +1,8 @@
 //! Shared SSH connection service and remote terminal adapter.
 mod connection;
 mod probe;
+mod tester;
 mod transport;
 pub use connection::{SshConnectionConfig, SshConnector, SshHandle, SshPrompts};
+pub use tester::SshConnectionTester;
 pub use transport::SshTerminalTransportProvider;
diff --git a/src/ssh/tester.rs b/src/ssh/tester.rs
new file mode 100644
index 0000000..504f38e
--- /dev/null
+++ b/src/ssh/tester.rs
@@ -0,0 +1,309 @@
+//! Log in once with the session form's values, for its 「测试连接」 button.
+use std::{
+    sync::{Arc, Mutex, OnceLock, Weak},
+    time::Duration,
+};
+
+use anyhow::Result;
+use tokio::sync::watch;
+use zeroize::Zeroizing;
+
+use super::connection::{
+    MissingCredential, SshConnectionConfig, SshConnector, SshPrompts, timeout_excluding_prompts,
+};
+use crate::{
+    connection::{
+        ConnectionPrompt, ConnectionPromptKind, ConnectionPromptReply, ConnectionTester, LoginTest,
+        TrustCallback,
+    },
+    secrets::{SecretRef, SecretStore, SharedSecretStore},
+};
+
+/// How long a test may take, not counting the time a person spends deciding
+/// whether to trust the host key.
+const TEST_TIMEOUT: Duration = Duration::from_secs(20);
+
+/// Tests a login through the same connector as terminals and SFTP, so host
+/// trust goes through the same file and lock.
+pub struct SshConnectionTester {
+    connector: SshConnector,
+}
+
+impl SshConnectionTester {
+    pub fn new(connector: SshConnector) -> Self {
+        Self { connector }
+    }
+}
+
+impl ConnectionTester for SshConnectionTester {
+    fn test(&self, request: LoginTest, trust: TrustCallback) -> Result<(), String> {
+        let runtime = tokio::runtime::Builder::new_current_thread()
+            .enable_all()
+            .build()
+            .map_err(|error| format!("无法启动连接测试：{error}"))?;
+        runtime.block_on(self.run(request, trust))
+    }
+}
+
+/// What the host-key checks said along the way, which the connect error alone
+/// does not tell apart.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+struct HostTrust {
+    declined: bool,
+    key_changed: bool,
+}
+
+impl SshConnectionTester {
+    async fn run(&self, request: LoginTest, trust: TrustCallback) -> Result<(), String> {
+        // Resolved apart from connecting, so a mistyped name says so instead
+        // of surfacing the resolver's own wording.
+        if tokio::net::lookup_host((request.host(), request.port()))
+            .await
+            .is_err()
+        {
+            return Err(format!("无法解析主机 {}", request.host()));
+        }
+
+        let config = SshConnectionConfig::new(
+            request.host(),
+            request.port(),
+            request.user(),
+            request.auth(),
+            request.key_path().map(Into::into),
+        );
+        let secrets: SharedSecretStore =
+            Arc::new(FormSecrets::new(&request, self.connector.secrets().clone()));
+        let host_trust = Arc::new(Mutex::new(HostTrust::default()));
+        let (_shutdown_tx, shutdown_rx) = watch::channel(false);
+        // The events callback answers the trust question through the broker,
+        // which does not exist yet when the callback is made.
+        let broker_slot: Arc<OnceLock<Weak<SshPrompts>>> = Arc::new(OnceLock::new());
+        let events = {
+            let trust = Arc::new(trust);
+            let host_trust = host_trust.clone();
+            let broker_slot = broker_slot.clone();
+            Arc::new(move |prompt: ConnectionPrompt| match prompt.kind() {
+                ConnectionPromptKind::UnknownHost(question) => {
+                    let (trust, host_trust, broker_slot) =
+                        (trust.clone(), host_trust.clone(), broker_slot.clone());
+                    let (request_id, question) = (prompt.request_id(), question.clone());
+                    // The answer takes a person; keep the connection's runtime
+                    // free while they decide.
+                    tokio::task::spawn_blocking(move || {
+                        let trusted = trust(question);
+                        if !trusted {
+                            lock(&host_trust).declined = true;
+                        }
+                        if let Some(broker) = broker_slot.get().and_then(Weak::upgrade) {
+                            broker.respond(
+                                request_id,
+                                if trusted {
+                                    ConnectionPromptReply::TrustAndSave
+                                } else {
+                                    ConnectionPromptReply::Cancel
+                                },
+                            );
+                        }
+                    });
+                    true
+                }
+                ConnectionPromptKind::HostKeyChanged(_) => {
+                    lock(&host_trust).key_changed = true;
+                    true
+                }
+                // Credential questions never get here: the broker is
+                // non-interactive and fails with a `MissingCredential`.
+                ConnectionPromptKind::Authentication(_) => false,
+            })
+        };
+        let broker = Arc::new(SshPrompts::new(events, shutdown_rx).non_interactive());
+        let _ = broker_slot.set(Arc::downgrade(&broker));
+
+        let connected = timeout_excluding_prompts(
+            self.connector
+                .connect_with(&config, broker.clone(), &secrets),
+            broker.prompt_activity_receiver(),
+            TEST_TIMEOUT,
+        )
+        .await
+        .and_then(|result| result);
+        match connected {
+            Ok((handle, _)) => {
+                let _ = handle
+                    .disconnect(russh::Disconnect::ByApplication, "connection test", "zh-CN")
+                    .await;
+                Ok(())
+            }
+            Err(error) => Err(describe_test_failure(&error, *lock(&host_trust))),
+        }
+    }
+}
+
+fn lock<T>(mutex: &Mutex<T>) -> std::sync::MutexGuard<'_, T> {
+    mutex.lock().unwrap_or_else(|error| error.into_inner())
+}
+
+/// Why a test failed, in the words the notification shows.
+fn describe_test_failure(error: &anyhow::Error, host_trust: HostTrust) -> String {
+    if host_trust.key_changed {
+        return "主机密钥与已保存的不一致，已阻止连接。请先核实服务器身份".into();
+    }
+    if host_trust.declined {
+        return "未信任该主机的密钥".into();
+    }
+    for cause in error.chain() {
+        if let Some(need) = cause.downcast_ref::<MissingCredential>() {
+            return need.to_string();
+        }
+        if let Some(io) = cause.downcast_ref::<std::io::Error>() {
+            return describe_connect_error(io);
+        }
+        match cause.downcast_ref::<russh::Error>() {
+            // russh wraps the socket's own error rather than chaining it.
+            Some(russh::Error::IO(io)) => return describe_connect_error(io),
+            Some(russh::Error::ConnectionTimeout) => return "连接超时".into(),
+            _ => {}
+        }
+    }
+    error.to_string()
+}
+
+/// A connect error in plain words. The common kinds get an explanation;
+/// anything else keeps the system's own description.
+fn describe_connect_error(error: &std::io::Error) -> String {
+    use std::io::ErrorKind;
+    match error.kind() {
+        ErrorKind::ConnectionRefused => "连接被拒绝，该端口上没有服务在监听".into(),
+        ErrorKind::TimedOut => "连接超时".into(),
+        ErrorKind::HostUnreachable | ErrorKind::NetworkUnreachable => "主机不可达".into(),
+        _ => format!("无法连接：{error}"),
+    }
+}
+
+/// The secrets a test logs in with. The form is authoritative for the login
+/// password and for the passphrase of the key it names, whether or not they
+/// were saved; anything else (a default key's passphrase) is read from the
+/// keychain. Nothing is ever written.
+struct FormSecrets {
+    password: (SecretRef, Option<Zeroizing<String>>),
+    passphrase: Option<(SecretRef, Option<Zeroizing<String>>)>,
+    fallback: SharedSecretStore,
+}
+
+impl FormSecrets {
+    fn new(request: &LoginTest, fallback: SharedSecretStore) -> Self {
+        let owned = |value: Option<&str>| value.map(|value| Zeroizing::new(value.to_string()));
+        Self {
+            password: (
+                SecretRef::password(request.user(), request.host(), request.port()),
+                owned(request.password()),
+            ),
+            passphrase: request
+                .key_path()
+                .map(|path| (SecretRef::passphrase(path), owned(request.passphrase()))),
+            fallback,
+        }
+    }
+}
+
+impl SecretStore for FormSecrets {
+    fn get(&self, secret: &SecretRef) -> anyhow::Result<Option<Zeroizing<String>>> {
+        if *secret == self.password.0 {
+            return Ok(self.password.1.clone());
+        }
+        if let Some((key, value)) = &self.passphrase
+            && secret == key
+        {
+            return Ok(value.clone());
+        }
+        self.fallback.get(secret)
+    }
+
+    fn set(&self, _: &SecretRef, _: &str) -> anyhow::Result<()> {
+        Ok(())
+    }
+
+    fn delete(&self, _: &SecretRef) -> anyhow::Result<()> {
+        Ok(())
+    }
+
+    fn is_available(&self) -> bool {
+        false
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::io::{Error, ErrorKind};
+
+    use anyhow::anyhow;
+
+    use super::{HostTrust, MissingCredential, describe_test_failure};
+
+    fn reason(error: anyhow::Error) -> String {
+        describe_test_failure(&error, HostTrust::default())
+    }
+
+    #[test]
+    fn host_trust_outranks_the_connect_error() {
+        let error = anyhow!("无法建立 SSH 连接，请检查主机、端口和主机密钥");
+        let changed = HostTrust {
+            key_changed: true,
+            ..HostTrust::default()
+        };
+        assert!(describe_test_failure(&error, changed).starts_with("主机密钥与已保存的不一致"));
+        let declined = HostTrust {
+            declined: true,
+            ..HostTrust::default()
+        };
+        assert_eq!(
+            describe_test_failure(&error, declined),
+            "未信任该主机的密钥"
+        );
+    }
+
+    #[test]
+    fn missing_credentials_name_what_was_wrong() {
+        assert_eq!(
+            reason(MissingCredential::Password { rejected: true }.into()),
+            "用户名或密码错误"
+        );
+        assert_eq!(
+            reason(MissingCredential::Password { rejected: false }.into()),
+            "未填写密码"
+        );
+        assert_eq!(
+            reason(MissingCredential::Passphrase { rejected: true }.into()),
+            "私钥口令错误"
+        );
+        assert_eq!(
+            reason(MissingCredential::Passphrase { rejected: false }.into()),
+            "私钥已加密，未填写口令"
+        );
+        assert!(reason(MissingCredential::KeyboardInteractive.into()).contains("键盘交互"));
+    }
+
+    #[test]
+    fn network_errors_are_explained_under_any_context() {
+        let refused = anyhow::Error::from(Error::from(ErrorKind::ConnectionRefused))
+            .context("无法建立 SSH 连接");
+        assert_eq!(reason(refused), "连接被拒绝，该端口上没有服务在监听");
+        assert_eq!(
+            reason(Error::from(ErrorKind::HostUnreachable).into()),
+            "主机不可达"
+        );
+        assert_eq!(reason(russh::Error::ConnectionTimeout.into()), "连接超时");
+        let wrapped =
+            anyhow::Error::from(russh::Error::IO(Error::from(ErrorKind::ConnectionRefused)))
+                .context("无法建立 SSH 连接");
+        assert_eq!(reason(wrapped), "连接被拒绝，该端口上没有服务在监听");
+    }
+
+    #[test]
+    fn anything_else_keeps_the_connector_wording() {
+        assert_eq!(
+            reason(anyhow!("服务器未接受指定的私钥")),
+            "服务器未接受指定的私钥"
+        );
+    }
+}
diff --git a/src/ssh/transport.rs b/src/ssh/transport.rs
index 8dbde6e..fd8fa49 100644
--- a/src/ssh/transport.rs
+++ b/src/ssh/transport.rs
@@ -323,7 +323,7 @@ async fn open_probe<H: client::Handler>(
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::secrets::{InMemorySecretStore, NoSecretStore, SecretStore as _};
+    use crate::secrets::{InMemorySecretStore, NoSecretStore, SecretRef, SecretStore as _};
     use crate::session::HostOs;
     use crate::ssh::probe::{PROBE_COMMAND, WINDOWS_PROBE_COMMAND};
     use crate::terminal::TerminalSecret;
@@ -910,6 +910,187 @@ mod tests {
         )
     }
 
+    /// Run a connection test the way the session form does, recording
+    /// whether (and about what) it asked to trust the host.
+    fn test_login(
+        request: crate::connection::LoginTest,
+        known_hosts: &Path,
+        keychain: Arc<InMemorySecretStore>,
+        trust: bool,
+    ) -> (Result<(), String>, Vec<String>) {
+        use crate::connection::ConnectionTester as _;
+        let asked = Arc::new(Mutex::new(Vec::new()));
+        let tester = crate::ssh::SshConnectionTester::new(SshConnector::new(known_hosts, keychain));
+        let result = tester.test(request, {
+            let asked = asked.clone();
+            Box::new(move |prompt| {
+                asked.lock().unwrap().push(prompt.fingerprint().to_string());
+                trust
+            })
+        });
+        let asked = asked.lock().unwrap().clone();
+        (result, asked)
+    }
+
+    fn login_request(port: u16) -> crate::connection::LoginTest {
+        crate::connection::LoginTest::new("127.0.0.1", port, "tester", AuthKind::Password)
+    }
+
+    #[test]
+    fn a_connection_test_logs_in_with_the_form_password_and_trusts_on_request() {
+        let Some(server) = start_server(TestAuth::Password) else {
+            eprintln!("loopback sockets are unavailable in this sandbox; skipping");
+            return;
+        };
+        let directory = tempfile::tempdir().unwrap();
+        let known_hosts = directory.path().join("known_hosts");
+        let keychain = Arc::new(InMemorySecretStore::default());
+
+        let (result, asked) = test_login(
+            login_request(server.port).with_password(TEST_PASSWORD),
+            &known_hosts,
+            keychain.clone(),
+            true,
+        );
+        assert_eq!(result, Ok(()));
+        assert_eq!(asked.len(), 1, "陌生主机应当问一次是否信任");
+        assert!(
+            std::fs::read_to_string(&known_hosts)
+                .unwrap()
+                .contains("127.0.0.1"),
+            "信任之后应当写进信任文件"
+        );
+        assert!(keychain.is_empty(), "测试连接不该写钥匙串");
+
+        // Trusted now: the second test asks nothing.
+        let (result, asked) = test_login(
+            login_request(server.port).with_password(TEST_PASSWORD),
+            &known_hosts,
+            keychain,
+            false,
+        );
+        assert_eq!(result, Ok(()));
+        assert!(asked.is_empty());
+    }
+
+    #[test]
+    fn a_wrong_form_password_fails_even_with_the_right_one_saved() {
+        let Some(server) = start_server(TestAuth::Password) else {
+            eprintln!("loopback sockets are unavailable in this sandbox; skipping");
+            return;
+        };
+        let directory = tempfile::tempdir().unwrap();
+        let known_hosts = directory.path().join("known_hosts");
+        // What the user reported: the keychain holds the working password,
+        // the form has been edited to a wrong one.
+        let keychain = Arc::new(InMemorySecretStore::default());
+        let saved = SecretRef::password("tester", "127.0.0.1", server.port);
+        keychain.set(&saved, TEST_PASSWORD).unwrap();
+
+        let (result, _) = test_login(
+            login_request(server.port).with_password("wrong-password"),
+            &known_hosts,
+            keychain.clone(),
+            true,
+        );
+        assert_eq!(result, Err("用户名或密码错误".to_string()));
+
+        let (result, _) = test_login(
+            login_request(server.port),
+            &known_hosts,
+            keychain.clone(),
+            true,
+        );
+        assert_eq!(result, Err("未填写密码".to_string()));
+        assert_eq!(
+            keychain.get(&saved).unwrap().as_deref().map(String::as_str),
+            Some(TEST_PASSWORD),
+            "保存的密码原样不动"
+        );
+        assert_eq!(keychain.len(), 1);
+    }
+
+    #[test]
+    fn declining_to_trust_fails_the_test_and_saves_nothing() {
+        let Some(server) = start_server(TestAuth::Password) else {
+            eprintln!("loopback sockets are unavailable in this sandbox; skipping");
+            return;
+        };
+        let directory = tempfile::tempdir().unwrap();
+        let known_hosts = directory.path().join("known_hosts");
+
+        let (result, asked) = test_login(
+            login_request(server.port).with_password(TEST_PASSWORD),
+            &known_hosts,
+            Arc::new(InMemorySecretStore::default()),
+            false,
+        );
+        assert_eq!(result, Err("未信任该主机的密钥".to_string()));
+        assert_eq!(asked.len(), 1);
+        assert!(
+            !known_hosts.exists()
+                || !std::fs::read_to_string(&known_hosts)
+                    .unwrap()
+                    .contains("127.0.0.1")
+        );
+    }
+
+    #[test]
+    fn a_changed_host_key_fails_the_test_without_asking() {
+        let Some(server) = start_server(TestAuth::Password) else {
+            eprintln!("loopback sockets are unavailable in this sandbox; skipping");
+            return;
+        };
+        let directory = tempfile::tempdir().unwrap();
+        let known_hosts = directory.path().join("known_hosts");
+        let mut rng = russh::keys::key::safe_rng();
+        let stale_key =
+            russh::keys::PrivateKey::random(&mut rng, russh::keys::Algorithm::Ed25519).unwrap();
+        learn_known_hosts_path(
+            "127.0.0.1",
+            server.port,
+            stale_key.public_key(),
+            &known_hosts,
+        )
+        .unwrap();
+
+        let (result, asked) = test_login(
+            login_request(server.port).with_password(TEST_PASSWORD),
+            &known_hosts,
+            Arc::new(InMemorySecretStore::default()),
+            true,
+        );
+        assert!(
+            result
+                .as_ref()
+                .is_err_and(|reason| reason.starts_with("主机密钥与已保存的不一致")),
+            "{result:?}"
+        );
+        assert!(asked.is_empty(), "密钥变了不该再问要不要信任");
+    }
+
+    #[test]
+    fn a_closed_port_fails_the_test_with_the_reason() {
+        let Ok(listener) = std::net::TcpListener::bind(("127.0.0.1", 0)) else {
+            eprintln!("loopback sockets are unavailable in this sandbox; skipping");
+            return;
+        };
+        let port = listener.local_addr().unwrap().port();
+        drop(listener);
+        let directory = tempfile::tempdir().unwrap();
+        let (result, asked) = test_login(
+            login_request(port).with_password(TEST_PASSWORD),
+            &directory.path().join("known_hosts"),
+            Arc::new(InMemorySecretStore::default()),
+            true,
+        );
+        assert_eq!(
+            result,
+            Err("连接被拒绝，该端口上没有服务在监听".to_string())
+        );
+        assert!(asked.is_empty());
+    }
+
     #[test]
     fn a_saved_password_connects_without_asking() {
         let Some(server) = start_server(TestAuth::Password) else {
diff --git a/src/workspace/workspace_view.rs b/src/workspace/workspace_view.rs
index 68f17d8..59b8085 100644
--- a/src/workspace/workspace_view.rs
+++ b/src/workspace/workspace_view.rs
@@ -28,6 +28,7 @@ use crate::app::{
     ToggleSessionPanel, ToggleTheme, ToggleUploadSelection, UploadSelectedFiles, ZoomIn, ZoomOut,
     ZoomReset,
 };
+use crate::connection::SharedConnectionTester;
 use crate::explorer::{ExplorerPanel, ExplorerPanelEvent, confirm_close_upload};
 use crate::session::{
     ConnectionState, GroupId, SessionId, SessionPanel, SessionStore, SessionStoreEvent,
@@ -100,6 +101,8 @@ pub struct Workspace {
     remote_terminal_provider: SharedRemoteTerminalTransportProvider,
     sftp_provider: SharedSftpTransportProvider,
     local_directory_provider: SharedLocalDirectoryProvider,
+    /// Backs the session dialog's 「测试连接」.
+    connection_tester: SharedConnectionTester,
     next_remote_terminal_id: u64,
     next_local_terminal_id: u64,
     /// The center tab displayed most recently; `CloseActiveTab` closes it.
@@ -132,6 +135,7 @@ impl Workspace {
         let remote = Arc::new(crate::ssh::SshTerminalTransportProvider::with_connector(
             connector.clone(),
         ));
+        let tester = Arc::new(crate::ssh::SshConnectionTester::new(connector.clone()));
         let sftp = Arc::new(SshSftpTransportProvider::new(
             connector,
             crate::app::data_dir().join("upload-resume"),
@@ -142,6 +146,7 @@ impl Workspace {
             local_terminal_factory,
             sftp,
             Arc::new(SystemLocalDirectoryProvider),
+            tester,
             window,
             cx,
         )
@@ -160,6 +165,7 @@ impl Workspace {
             crate::app::data_dir().join("known_hosts"),
             store.read(cx).secrets(),
         );
+        let tester = Arc::new(crate::ssh::SshConnectionTester::new(connector.clone()));
         let sftp = Arc::new(SshSftpTransportProvider::new(
             connector,
             crate::app::data_dir().join("upload-resume"),
@@ -170,18 +176,23 @@ impl Workspace {
             local_terminal_factory,
             sftp,
             Arc::new(SystemLocalDirectoryProvider),
+            tester,
             window,
             cx,
         )
     }
 
     /// Inject every filesystem and transport service; tests require neither a server nor a keychain.
+    // One parameter per injected service, which is the point of this
+    // constructor; bundling them would only move the list elsewhere.
+    #[allow(clippy::too_many_arguments)]
     pub fn new_with_services(
         store: Entity<SessionStore>,
         remote_terminal_provider: SharedRemoteTerminalTransportProvider,
         local_terminal_factory: SharedTerminalTransportFactory,
         sftp_provider: SharedSftpTransportProvider,
         local_directory_provider: SharedLocalDirectoryProvider,
+        connection_tester: SharedConnectionTester,
         window: &mut Window,
         cx: &mut Context<Self>,
     ) -> Self {
@@ -303,6 +314,7 @@ impl Workspace {
             remote_terminal_provider,
             sftp_provider,
             local_directory_provider,
+            connection_tester,
             next_remote_terminal_id,
             next_local_terminal_id: 1,
             active_tab: None,
@@ -408,13 +420,7 @@ impl Workspace {
         let workspace = cx.entity().downgrade();
         match prompt.kind().clone() {
             TerminalPromptKind::UnknownHost(prompt) => {
-                let description = format!(
-                    "主机：{}:{}\n算法：{}\nSHA-256 指纹：{}\n\n请先确认该指纹来自可信渠道。",
-                    prompt.host(),
-                    prompt.port(),
-                    prompt.algorithm(),
-                    prompt.fingerprint(),
-                );
+                let description = prompt.description();
                 window.open_alert_dialog(cx, move |alert, _, _| {
                     alert
                         .title("首次连接此主机")
@@ -1154,7 +1160,14 @@ impl Workspace {
     }
 
     fn on_new_session(&mut self, _: &NewSession, window: &mut Window, cx: &mut Context<Self>) {
-        open_session_dialog(None, None, self.store.clone(), window, cx);
+        open_session_dialog(
+            None,
+            None,
+            self.store.clone(),
+            self.connection_tester.clone(),
+            window,
+            cx,
+        );
     }
 
     fn on_edit_session(
@@ -1164,7 +1177,14 @@ impl Workspace {
         cx: &mut Context<Self>,
     ) {
         if self.store.read(cx).session(action.0).is_some() {
-            open_session_dialog(Some(action.0), None, self.store.clone(), window, cx);
+            open_session_dialog(
+                Some(action.0),
+                None,
+                self.store.clone(),
+                self.connection_tester.clone(),
+                window,
+                cx,
+            );
         }
     }
 
@@ -1268,7 +1288,14 @@ impl Workspace {
         window: &mut Window,
         cx: &mut Context<Self>,
     ) {
-        open_session_dialog(None, Some(action.0), self.store.clone(), window, cx);
+        open_session_dialog(
+            None,
+            Some(action.0),
+            self.store.clone(),
+            self.connection_tester.clone(),
+            window,
+            cx,
+        );
     }
 
     fn on_new_group(&mut self, _: &NewGroup, window: &mut Window, cx: &mut Context<Self>) {
diff --git a/tests/ui.rs b/tests/ui.rs
index cbb0238..e12c995 100644
--- a/tests/ui.rs
+++ b/tests/ui.rs
@@ -1,13 +1,11 @@
 //! UI integration tests: the production `Workspace` rendered in a headless
 //! window, driven through real pointer and keyboard events.
 
-use std::io::Write as _;
-use std::net::TcpListener;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::{Arc, Mutex, mpsc};
 use std::time::Duration;
 
-use gpui_kit::component::{ActiveTheme as _, Root};
+use gpui_kit::component::{ActiveTheme as _, Root, WindowExt as _};
 use gpui_kit::test::{TestAppContextExt, TestWindowExt};
 use gpui_kit::{
     AppContext as _, ClipboardItem, ElementId, Entity, InputEvent as _, MouseButton,
@@ -19,6 +17,7 @@ use shellr::app::{
     CopySessionHost, DeleteGroup, DeleteSession, EditSession, ExpandAllGroups, NewLocalTerminal,
     NewSessionInGroup, OpenExplorer, RenameGroup, RenameTerminal,
 };
+use shellr::connection::{ConnectionPromptKind, ConnectionTester, LoginTest, TrustCallback};
 use shellr::secrets::{InMemorySecretStore, SecretRef, SecretStore as _};
 use shellr::session::{
     AuthKind, ConnectionState, GroupDraft, GroupId, HostOs, SessionDatabase, SessionDraft,
@@ -58,6 +57,15 @@ fn open_workspace(cx: &mut TestAppContext) -> (WindowHandle<Root>, Entity<Worksp
 fn open_workspace_with_store(
     cx: &mut TestAppContext,
     store: SessionStore,
+) -> (WindowHandle<Root>, Entity<Workspace>) {
+    open_workspace_with_tester(cx, store, Arc::new(FakeConnectionTester::default()))
+}
+
+/// Same, with the session dialog's connection test answered by `tester`.
+fn open_workspace_with_tester(
+    cx: &mut TestAppContext,
+    store: SessionStore,
+    tester: Arc<FakeConnectionTester>,
 ) -> (WindowHandle<Root>, Entity<Workspace>) {
     cx.update(shellr::init);
     let mut workspace = None;
@@ -73,6 +81,7 @@ fn open_workspace_with_store(
                 Arc::new(FakeTerminalFactory::default()),
                 Arc::new(FakeSftpProvider::default()),
                 Arc::new(FakeLocalDirectory),
+                tester.clone(),
                 window,
                 cx,
             )
@@ -83,6 +92,92 @@ fn open_workspace_with_store(
     (handle, workspace.expect("workspace created"))
 }
 
+/// `(host, port, user, password)` of one connection test.
+type TestedLogin = (String, u16, String, Option<String>);
+
+/// Stands in for the SSH login behind 「测试连接」: records what the form sent,
+/// optionally asks to trust a made-up host key, and answers with `result`.
+struct FakeConnectionTester {
+    asks_trust: bool,
+    result: Result<(), String>,
+    requests: Mutex<Vec<TestedLogin>>,
+    trust_answers: Mutex<Vec<bool>>,
+}
+
+impl Default for FakeConnectionTester {
+    fn default() -> Self {
+        Self {
+            asks_trust: false,
+            result: Ok(()),
+            requests: Mutex::default(),
+            trust_answers: Mutex::default(),
+        }
+    }
+}
+
+impl FakeConnectionTester {
+    fn failing(reason: &str) -> Self {
+        Self {
+            result: Err(reason.to_string()),
+            ..Self::default()
+        }
+    }
+
+    fn asking_trust() -> Self {
+        Self {
+            asks_trust: true,
+            ..Self::default()
+        }
+    }
+
+    fn requests(&self) -> Vec<TestedLogin> {
+        self.requests
+            .lock()
+            .unwrap_or_else(|error| error.into_inner())
+            .clone()
+    }
+
+    fn trust_answers(&self) -> Vec<bool> {
+        self.trust_answers
+            .lock()
+            .unwrap_or_else(|error| error.into_inner())
+            .clone()
+    }
+}
+
+impl ConnectionTester for FakeConnectionTester {
+    fn test(&self, request: LoginTest, trust: TrustCallback) -> Result<(), String> {
+        self.requests
+            .lock()
+            .unwrap_or_else(|error| error.into_inner())
+            .push((
+                request.host().to_string(),
+                request.port(),
+                request.user().to_string(),
+                request.password().map(str::to_string),
+            ));
+        if self.asks_trust {
+            let ConnectionPromptKind::UnknownHost(prompt) = ConnectionPromptKind::unknown_host(
+                request.host(),
+                request.port(),
+                "ssh-ed25519",
+                "SHA256:test-fingerprint",
+            ) else {
+                unreachable!("unknown_host builds an UnknownHost prompt");
+            };
+            let trusted = trust(prompt);
+            self.trust_answers
+                .lock()
+                .unwrap_or_else(|error| error.into_inner())
+                .push(trusted);
+            if !trusted {
+                return Err("未信任该主机的密钥".to_string());
+            }
+        }
+        self.result.clone()
+    }
+}
+
 #[derive(Clone, Copy, Default)]
 enum FakeBehavior {
     #[default]
@@ -238,6 +333,7 @@ fn open_workspace_with_factory(
                 factory.clone(),
                 Arc::new(FakeSftpProvider::default()),
                 Arc::new(FakeLocalDirectory),
+                Arc::new(FakeConnectionTester::default()),
                 window,
                 cx,
             )
@@ -265,6 +361,7 @@ fn open_workspace_with_remote_factory(
                 Arc::new(FakeTerminalFactory::default()),
                 Arc::new(FakeSftpProvider::default()),
                 Arc::new(FakeLocalDirectory),
+                Arc::new(FakeConnectionTester::default()),
                 window,
                 cx,
             )
@@ -878,17 +975,75 @@ async fn new_session_dialog_validates_then_inserts(cx: &mut TestAppContext) {
     });
 }
 
+/// What the user reported: the keychain has the working password, the edit
+/// dialog's field has been changed to a wrong one, and 「测试连接」 must try the
+/// field — without saving anything.
 #[gpui_kit::test]
-async fn session_dialog_tests_ssh_service_without_saving(cx: &mut TestAppContext) {
-    let listener = TcpListener::bind(("127.0.0.1", 0)).unwrap();
-    let port = listener.local_addr().unwrap().port();
-    let (reply, resume) = mpsc::channel();
-    let server = std::thread::spawn(move || {
-        let (mut stream, _) = listener.accept().unwrap();
-        resume.recv_timeout(Duration::from_secs(3)).unwrap();
-        stream.write_all(b"SSH-2.0-test-server\r\n").unwrap();
+async fn testing_a_connection_logs_in_with_what_the_form_shows(cx: &mut TestAppContext) {
+    let secrets = Arc::new(InMemorySecretStore::default());
+    let (store, id, endpoint) = store_with_secrets(secrets.clone());
+    secrets.set(&endpoint, "hunter2").unwrap();
+    let tester = Arc::new(FakeConnectionTester::failing("用户名或密码错误"));
+    let (handle, workspace) = open_workspace_with_tester(cx, store, tester.clone());
+
+    cx.update_window(handle.into(), |_, window, cx| {
+        window.render_frame(cx);
+        window.dispatch_action(Box::new(EditSession(id)), cx);
+    })
+    .unwrap();
+    // The saved password is read on a background thread, then fills the field.
+    cx.run_until_parked();
+    cx.update_window(handle.into(), |_, window, cx| {
+        window.render_frame(cx);
+        window.click("session-password", cx);
+        window.press("cmd-a", cx);
+        window.input("wrong-password", cx);
+        window.click("session-port", cx);
+        window.press("cmd-a", cx);
+        window.input("2222", cx);
+        window.click("test-connection", cx);
+    })
+    .unwrap();
+    cx.wait_for(handle.into(), Duration::from_secs(3), |window, cx| {
+        window.render_frame(cx);
+        window.notifications(cx).len() == 1
+    })
+    .await;
+
+    assert_eq!(
+        tester.requests(),
+        [(
+            "10.0.2.5".to_string(),
+            2222,
+            "postgres".to_string(),
+            Some("wrong-password".to_string())
+        )]
+    );
+    cx.update_window(handle.into(), |_, window, cx| {
+        window.render_frame(cx);
+        // Nothing was saved, and the dialog stays open to fix the field.
+        assert!(window.find("commit").visible());
+    })
+    .unwrap();
+    cx.update(|cx| {
+        let store = workspace.read(cx).store().read(cx);
+        assert_eq!(store.session(id).unwrap().port, 22);
     });
-    let (handle, workspace) = open_workspace_with_store(cx, SessionStore::empty());
+    assert_eq!(
+        secrets
+            .get(&endpoint)
+            .unwrap()
+            .as_deref()
+            .map(String::as_str),
+        Some("hunter2"),
+        "测试连接不写钥匙串"
+    );
+}
+
+#[gpui_kit::test]
+async fn a_connection_test_needs_a_host_and_a_user_first(cx: &mut TestAppContext) {
+    let tester = Arc::new(FakeConnectionTester::default());
+    let (handle, _) = open_workspace_with_tester(cx, SessionStore::empty(), tester.clone());
 
     cx.update_window(handle.into(), |_, window, cx| {
         window.render_frame(cx);
@@ -903,45 +1058,102 @@ async fn session_dialog_tests_ssh_service_without_saving(cx: &mut TestAppContext
         let commit = window.find("commit").bounds();
         assert!(test.right() < cancel.left());
         assert!(cancel.right() < commit.left());
-        assert!(commit.size.width < window.find("session-host").bounds().size.width);
-
+        assert!(window.notifications(cx).is_empty());
         window.click("test-connection", cx);
     })
     .unwrap();
+    cx.run_until_parked();
     cx.update_window(handle.into(), |_, window, cx| {
         window.render_frame(cx);
-        assert_eq!(
-            window.find("connection-test-result").label(),
-            Some("请输入主机")
-        );
+        // Reported at once as a failed test; the form shows no result of its own.
+        assert_eq!(window.notifications(cx).len(), 1);
+        assert!(window.try_find("form-error").is_none());
         window.click("session-host", cx);
-        window.input("127.0.0.1", cx);
-        window.click("session-port", cx);
+        window.input("10.0.3.7", cx);
+        window.click("session-user", cx);
         #[cfg(target_os = "macos")]
         window.press("cmd-a", cx);
         #[cfg(not(target_os = "macos"))]
         window.press("ctrl-a", cx);
-        window.input(&port.to_string(), cx);
+        window.press("backspace", cx);
         window.click("test-connection", cx);
     })
     .unwrap();
+    cx.run_until_parked();
     cx.update_window(handle.into(), |_, window, cx| {
         window.render_frame(cx);
-        assert!(window.find("test-connection").visible());
-        assert!(window.try_find("connection-test-result").is_none());
+        assert_eq!(window.notifications(cx).len(), 2, "没有用户名也不该去连");
+    })
+    .unwrap();
+    assert!(tester.requests().is_empty());
+}
+
+#[gpui_kit::test]
+async fn a_first_seen_host_key_is_put_to_the_user_above_the_session_dialog(
+    cx: &mut TestAppContext,
+) {
+    let tester = Arc::new(FakeConnectionTester::asking_trust());
+    let (store, id) = one_session_store(AuthKind::Password);
+    let (handle, _) = open_workspace_with_tester(cx, store, tester.clone());
+
+    // Trust: the question reaches the tester as a yes.
+    cx.update_window(handle.into(), |_, window, cx| {
+        window.render_frame(cx);
+        window.dispatch_action(Box::new(EditSession(id)), cx);
+    })
+    .unwrap();
+    cx.run_until_parked();
+    cx.update_window(handle.into(), |_, window, cx| {
+        window.render_frame(cx);
+        window.click("test-connection", cx);
     })
     .unwrap();
-    reply.send(()).unwrap();
     cx.wait_for(handle.into(), Duration::from_secs(3), |window, cx| {
         window.render_frame(cx);
-        window
-            .try_find("connection-test-result")
-            .and_then(|result| result.label().map(str::to_string))
-            .is_some_and(|message| message.contains("SSH 服务可达"))
+        window.try_find("ok").is_some()
     })
     .await;
-    server.join().unwrap();
-    cx.update(|cx| assert!(workspace.read(cx).store().read(cx).sessions().is_empty()));
+    cx.update_window(handle.into(), |_, window, cx| {
+        window.render_frame(cx);
+        window.click("ok", cx);
+    })
+    .unwrap();
+    cx.wait_for(handle.into(), Duration::from_secs(3), |window, cx| {
+        window.render_frame(cx);
+        window.notifications(cx).len() == 1
+    })
+    .await;
+    assert_eq!(tester.trust_answers(), [true]);
+
+    // Escape dismisses the question, which declines it; the session dialog
+    // underneath stays open.
+    cx.update_window(handle.into(), |_, window, cx| {
+        window.render_frame(cx);
+        assert!(window.try_find("ok").is_none());
+        window.click("test-connection", cx);
+    })
+    .unwrap();
+    cx.wait_for(handle.into(), Duration::from_secs(3), |window, cx| {
+        window.render_frame(cx);
+        window.try_find("ok").is_some()
+    })
+    .await;
+    cx.update_window(handle.into(), |_, window, cx| {
+        window.render_frame(cx);
+        window.press("escape", cx);
+    })
+    .unwrap();
+    cx.wait_for(handle.into(), Duration::from_secs(3), |window, cx| {
+        window.render_frame(cx);
+        window.notifications(cx).len() == 2
+    })
+    .await;
+    assert_eq!(tester.trust_answers(), [true, false]);
+    cx.update_window(handle.into(), |_, window, cx| {
+        window.render_frame(cx);
+        assert!(window.find("commit").visible());
+    })
+    .unwrap();
 }
 
 #[gpui_kit::test]
@@ -2996,6 +3208,7 @@ fn open_workspace_with_sftp(
                 Arc::new(FakeTerminalFactory::default()),
                 provider,
                 Arc::new(FakeLocalDirectory),
+                Arc::new(FakeConnectionTester::default()),
                 window,
                 cx,
             )