Fix tests to wrap all calls changing the UI with act. (#12268)

packages/cli/test-setup.ts

@@ -4,9 +4,61 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import { vi, beforeEach, afterEach } from 'vitest';
+import { format } from 'node:util';
+
+global.IS_REACT_ACT_ENVIRONMENT = true;
+
 // Unset NO_COLOR environment variable to ensure consistent theme behavior between local and CI test runs
 if (process.env.NO_COLOR !== undefined) {
   delete process.env.NO_COLOR;
 }
 
 import './src/test-utils/customMatchers.js';
+
+let consoleErrorSpy: vi.SpyInstance;
+let actWarnings: Array<{ message: string; stack: string }> = [];
+
+beforeEach(() => {
+  actWarnings = [];
+  consoleErrorSpy = vi.spyOn(console, 'error').mockImplementation((...args) => {
+    const firstArg = args[0];
+    if (
+      typeof firstArg === 'string' &&
+      firstArg.includes('was not wrapped in act(...)')
+    ) {
+      const stackLines = (new Error().stack || '').split('\n');
+      let lastReactFrameIndex = -1;
+
+      // Find the index of the last frame that comes from react-reconciler
+      for (let i = 0; i < stackLines.length; i++) {
+        if (stackLines[i].includes('react-reconciler')) {
+          lastReactFrameIndex = i;
+        }
+      }
+
+      // If we found react-reconciler frames, start the stack trace after the last one.
+      // Otherwise, just strip the first line (which is the Error message itself).
+      const relevantStack =
+        lastReactFrameIndex !== -1
+          ? stackLines.slice(lastReactFrameIndex + 1).join('\n')
+          : stackLines.slice(1).join('\n');
+
+      actWarnings.push({
+        message: format(...args),
+        stack: relevantStack,
+      });
+    }
+  });
+});
+
+afterEach(() => {
+  consoleErrorSpy.mockRestore();
+
+  if (actWarnings.length > 0) {
+    const messages = actWarnings
+      .map(({ message, stack }) => `${message}\n${stack}`)
+      .join('\n\n');
+    throw new Error(`Failing test due to "act(...)" warnings:\n${messages}`);
+  }
+});