test: deepen and complete project-wide test coverage (#297)

* test: deepen coverage for health doctor provider and tunnels

* test: add broad trait and module re-export coverage

src/tunnel/tailscale.rs

@@ -100,3 +100,34 @@ impl Tunnel for TailscaleTunnel {
             .and_then(|g| g.as_ref().map(|tp| tp.public_url.clone()))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn constructor_stores_hostname_and_mode() {
+        let tunnel = TailscaleTunnel::new(true, Some("myhost.tailnet.ts.net".into()));
+        assert!(tunnel.funnel);
+        assert_eq!(tunnel.hostname.as_deref(), Some("myhost.tailnet.ts.net"));
+    }
+
+    #[test]
+    fn public_url_is_none_before_start() {
+        let tunnel = TailscaleTunnel::new(false, None);
+        assert!(tunnel.public_url().is_none());
+    }
+
+    #[tokio::test]
+    async fn health_check_is_false_before_start() {
+        let tunnel = TailscaleTunnel::new(false, None);
+        assert!(!tunnel.health_check().await);
+    }
+
+    #[tokio::test]
+    async fn stop_without_started_process_is_ok() {
+        let tunnel = TailscaleTunnel::new(false, None);
+        let result = tunnel.stop().await;
+        assert!(result.is_ok());
+    }
+}