From 034156ca926bc0af29a5709cff07779566db8b10 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mike=20Kr=C3=BCger?= <mikkrg@microsoft.com>
Date: Thu, 6 Aug 2026 13:18:27 +0200
Subject: [PATCH] Add unit tests for registerTerminalResizeHandler (debounce,
 no-op skip, error handling)

---
 .../CloudShellTerminalCore.test.tsx           | 119 ++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 src/Explorer/Tabs/CloudShellTab/CloudShellTerminalCore.test.tsx

diff --git a/src/Explorer/Tabs/CloudShellTab/CloudShellTerminalCore.test.tsx b/src/Explorer/Tabs/CloudShellTab/CloudShellTerminalCore.test.tsx
new file mode 100644
index 000000000..f5f67c3de
--- /dev/null
+++ b/src/Explorer/Tabs/CloudShellTab/CloudShellTerminalCore.test.tsx
@@ -0,0 +1,119 @@
+import { Terminal } from "xterm";
+import { registerTerminalResizeHandler } from "./CloudShellTerminalCore";
+import { resizeTerminal } from "./Data/CloudShellClient";
+
+// Mock the CloudShell client so we can assert on backend resize calls without any network access.
+jest.mock("./Data/CloudShellClient");
+
+const mockResizeTerminal = resizeTerminal as jest.Mock;
+
+const CONSOLE_URI = "https://shell.azure.com/console123";
+const TERMINAL_ID = "terminal-id";
+const DEBOUNCE_MS = 300;
+
+type ResizeListener = (size: { cols: number; rows: number }) => void;
+
+interface MockTerminal {
+  cols: number;
+  rows: number;
+  onResize: (listener: ResizeListener) => void;
+  emitResize: (size: { cols: number; rows: number }) => void;
+}
+
+const createMockTerminal = (cols: number, rows: number): MockTerminal => {
+  let listener: ResizeListener | undefined;
+  return {
+    cols,
+    rows,
+    onResize: (cb: ResizeListener) => {
+      listener = cb;
+    },
+    emitResize: (size: { cols: number; rows: number }) => listener?.(size),
+  };
+};
+
+const registerHandler = (terminal: MockTerminal): void =>
+  registerTerminalResizeHandler(terminal as unknown as Terminal, CONSOLE_URI, TERMINAL_ID);
+
+describe("registerTerminalResizeHandler", () => {
+  beforeEach(() => {
+    jest.useFakeTimers();
+    mockResizeTerminal.mockReset();
+    mockResizeTerminal.mockResolvedValue(undefined);
+  });
+
+  afterEach(() => {
+    jest.clearAllTimers();
+    jest.useRealTimers();
+  });
+
+  it("does not notify the backend when the dimensions are unchanged", () => {
+    const terminal = createMockTerminal(80, 24);
+    registerHandler(terminal);
+
+    terminal.emitResize({ cols: 80, rows: 24 });
+    jest.advanceTimersByTime(DEBOUNCE_MS);
+
+    expect(mockResizeTerminal).not.toHaveBeenCalled();
+  });
+
+  it("notifies the backend with the new dimensions after the debounce interval", () => {
+    const terminal = createMockTerminal(80, 24);
+    registerHandler(terminal);
+
+    terminal.emitResize({ cols: 120, rows: 40 });
+    // Nothing should be sent until the debounce interval elapses.
+    expect(mockResizeTerminal).not.toHaveBeenCalled();
+
+    jest.advanceTimersByTime(DEBOUNCE_MS);
+
+    expect(mockResizeTerminal).toHaveBeenCalledTimes(1);
+    expect(mockResizeTerminal).toHaveBeenCalledWith(CONSOLE_URI, TERMINAL_ID, { cols: 120, rows: 40 });
+  });
+
+  it("debounces rapid resizes into a single call with the latest dimensions", () => {
+    const terminal = createMockTerminal(80, 24);
+    registerHandler(terminal);
+
+    terminal.emitResize({ cols: 100, rows: 30 });
+    terminal.emitResize({ cols: 110, rows: 35 });
+    terminal.emitResize({ cols: 120, rows: 40 });
+
+    jest.advanceTimersByTime(DEBOUNCE_MS);
+
+    expect(mockResizeTerminal).toHaveBeenCalledTimes(1);
+    expect(mockResizeTerminal).toHaveBeenCalledWith(CONSOLE_URI, TERMINAL_ID, { cols: 120, rows: 40 });
+  });
+
+  it("sends a separate call for each resize that is spaced beyond the debounce interval", () => {
+    const terminal = createMockTerminal(80, 24);
+    registerHandler(terminal);
+
+    terminal.emitResize({ cols: 100, rows: 30 });
+    jest.advanceTimersByTime(DEBOUNCE_MS);
+
+    terminal.emitResize({ cols: 120, rows: 40 });
+    jest.advanceTimersByTime(DEBOUNCE_MS);
+
+    expect(mockResizeTerminal).toHaveBeenCalledTimes(2);
+    expect(mockResizeTerminal).toHaveBeenNthCalledWith(1, CONSOLE_URI, TERMINAL_ID, { cols: 100, rows: 30 });
+    expect(mockResizeTerminal).toHaveBeenNthCalledWith(2, CONSOLE_URI, TERMINAL_ID, { cols: 120, rows: 40 });
+  });
+
+  it("swallows backend resize errors and logs a warning", async () => {
+    const warnSpy = jest.spyOn(console, "warn").mockImplementation(() => undefined);
+    mockResizeTerminal.mockRejectedValueOnce(new Error("boom"));
+    const terminal = createMockTerminal(80, 24);
+    registerHandler(terminal);
+
+    terminal.emitResize({ cols: 120, rows: 40 });
+    jest.advanceTimersByTime(DEBOUNCE_MS);
+    // Flush the microtask queue so the rejected promise's .catch handler runs.
+    await Promise.resolve();
+
+    expect(mockResizeTerminal).toHaveBeenCalledTimes(1);
+    expect(warnSpy).toHaveBeenCalledWith("CloudShell: failed to resize backend terminal", expect.any(Error));
+
+    warnSpy.mockRestore();
+  });
+});