[Tests] Add unit tests for flushPromises utility

packages/cli-kit/src/public/node/promises.test.ts

@@ -0,0 +1,54 @@
+import {flushPromises} from './promises.js'
+import {describe, expect, test} from 'vitest'
+
+describe('flushPromises', () => {
+  test('waits for microtasks to complete', async () => {
+    // Given
+    let result = ''
+    const _promise = Promise.resolve().then(() => {
+      result += 'microtask'
+    })
+
+    // When
+    await flushPromises()
+    result += ' flushed'
+
+    // Then
+    expect(result).toBe('microtask flushed')
+  })
+
+  test('waits for multiple nested microtasks', async () => {
+    // Given
+    let result = ''
+    const _promise = Promise.resolve()
+      .then(() => {
+        result += '1'
+        return 'intermediate'
+      })
+      .then(() => {
+        result += '2'
+      })
+
+    // When
+    await flushPromises()
+    result += ' flushed'
+
+    // Then
+    expect(result).toBe('12 flushed')
+  })
+
+  test('waits for macrotasks scheduled with setImmediate', async () => {
+    // Given
+    let result = ''
+    setImmediate(() => {
+      result += 'macrotask'
+    })
+
+    // When
+    await flushPromises()
+    result += ' flushed'
+
+    // Then
+    expect(result).toBe('macrotask flushed')
+  })
+})