[Tests] Add unit tests for theme batching utilities

packages/theme/src/cli/utilities/batching.test.ts

@@ -0,0 +1,91 @@
+import {batchedRequests, batchedTasks} from './batching.js'
+import {describe, expect, test, vi} from 'vitest'
+
+describe('batchedRequests', () => {
+  test('splits items into batches of the given size, keeping a smaller final batch', async () => {
+    // Given
+    const fn = vi.fn(async (_batch: number[]) => undefined)
+
+    // When
+    await Promise.all(batchedRequests([1, 2, 3, 4, 5], 2, fn))
+
+    // Then
+    expect(fn.mock.calls.map(([batch]) => batch)).toEqual([[1, 2], [3, 4], [5]])
+  })
+
+  test('returns one promise per batch resolving to the callback result', async () => {
+    // Given
+    const fn = async (batch: number[]) => batch.length
+
+    // When
+    const requests = batchedRequests([1, 2, 3, 4, 5], 2, fn)
+
+    // Then
+    await expect(Promise.all(requests)).resolves.toEqual([2, 2, 1])
+  })
+
+  test('does not invoke the callback when there are no items', () => {
+    // Given
+    const fn = vi.fn(async () => undefined)
+
+    // When
+    const requests = batchedRequests([], 2, fn)
+
+    // Then
+    expect(requests).toEqual([])
+    expect(fn).not.toHaveBeenCalled()
+  })
+
+  test('emits a single batch when the batch size exceeds the number of items', async () => {
+    // Given
+    const fn = vi.fn(async () => undefined)
+
+    // When
+    await Promise.all(batchedRequests([1, 2], 50, fn))
+
+    // Then
+    expect(fn).toHaveBeenCalledOnce()
+    expect(fn).toHaveBeenCalledWith([1, 2])
+  })
+})
+
+describe('batchedTasks', () => {
+  test('builds one task per batch and passes the index of the first item in the batch', () => {
+    // Given
+    const items = ['a', 'b', 'c', 'd', 'e']
+
+    // When
+    const tasks = batchedTasks(items, 2, (batch, start) => ({
+      title: `${start}:${batch.join('')}`,
+      task: async () => {},
+    }))
+
+    // Then
+    expect(tasks.map((task) => task.title)).toEqual(['0:ab', '2:cd', '4:e'])
+  })
+
+  test('returns no tasks when there are no items', () => {
+    // Given
+    const fn = vi.fn(() => ({title: 'unused', task: async () => {}}))
+
+    // When
+    const tasks = batchedTasks([], 2, fn)
+
+    // Then
+    expect(tasks).toEqual([])
+    expect(fn).not.toHaveBeenCalled()
+  })
+
+  test('defers work until a task is run', async () => {
+    // Given
+    const run = vi.fn(async (_batch: number[]) => undefined)
+
+    // When
+    const tasks = batchedTasks([1, 2], 1, (batch) => ({title: 'download', task: async () => run(batch)}))
+
+    // Then
+    expect(run).not.toHaveBeenCalled()
+    await Promise.all(tasks.map((task) => task.task()))
+    expect(run.mock.calls.map(([batch]) => batch)).toEqual([[1], [2]])
+  })
+})