test: added tests for batcher

Author: wyattjoh

packages/next/src/lib/batcher.test.ts

@@ -0,0 +1,78 @@
+import { Batcher } from './batcher'
+
+describe('Batcher', () => {
+  describe('batch', () => {
+    it('should execute the work function immediately', async () => {
+      const batcher = Batcher.create<string, number>()
+      const workFn = jest.fn().mockResolvedValue(42)
+
+      const result = await batcher.batch('key', workFn)
+
+      expect(result).toBe(42)
+      expect(workFn).toHaveBeenCalledTimes(1)
+    })
+
+    it('should batch multiple calls to the same key', async () => {
+      const batcher = Batcher.create<string, number>()
+      const workFn = jest.fn().mockResolvedValue(42)
+
+      const result1 = batcher.batch('key', workFn)
+      const result2 = batcher.batch('key', workFn)
+
+      expect(result1).toBeInstanceOf(Promise)
+      expect(result2).toBeInstanceOf(Promise)
+      expect(workFn).toHaveBeenCalledTimes(1)
+
+      const [value1, value2] = await Promise.all([result1, result2])
+
+      expect(value1).toBe(42)
+      expect(value2).toBe(42)
+      expect(workFn).toHaveBeenCalledTimes(1)
+    })
+
+    it('should not batch calls to different keys', async () => {
+      const batcher = Batcher.create<string, string>()
+      const workFn = jest.fn((key) => key)
+
+      const result1 = batcher.batch('key1', workFn)
+      const result2 = batcher.batch('key2', workFn)
+
+      expect(result1).toBeInstanceOf(Promise)
+      expect(result2).toBeInstanceOf(Promise)
+      expect(workFn).toHaveBeenCalledTimes(2)
+
+      const [value1, value2] = await Promise.all([result1, result2])
+
+      expect(value1).toBe('key1')
+      expect(value2).toBe('key2')
+      expect(workFn).toHaveBeenCalledTimes(2)
+    })
+
+    it('should use the cacheKeyFn to generate cache keys', async () => {
+      const cacheKeyFn = jest.fn().mockResolvedValue('cache-key')
+      const batcher = Batcher.create<string, number>({ cacheKeyFn })
+      const workFn = jest.fn().mockResolvedValue(42)
+
+      const result = await batcher.batch('key', workFn)
+
+      expect(result).toBe(42)
+      expect(cacheKeyFn).toHaveBeenCalledWith('key')
+      expect(workFn).toHaveBeenCalledTimes(1)
+    })
+
+    it('should use the schedulerFn to schedule work', async () => {
+      const schedulerFn = jest.fn().mockImplementation((fn) => fn())
+      const batcher = Batcher.create<string, number>({ schedulerFn })
+      const workFn = jest.fn().mockResolvedValue(42)
+
+      const results = await Promise.all([
+        batcher.batch('key', workFn),
+        batcher.batch('key', workFn),
+        batcher.batch('key', workFn),
+      ])
+
+      expect(results).toEqual([42, 42, 42])
+      expect(workFn).toHaveBeenCalledTimes(1)
+    })
+  })
+})