Adding tests for delay

src/util/delay.test.js

@@ -0,0 +1,26 @@
+import delay from './delay'
+
+jest.useFakeTimers()
+
+describe('delay', () => {
+    test('should set a timer with the given delay', () => {
+        delay(1000)
+        expect(setTimeout.mock.calls.length).toBe(1)
+        expect(setTimeout.mock.calls[0][1]).toBe(1000)
+    })
+
+    test('should return a promise which resolves after the timer finishes', async () => {
+        const assertFunc = jest.fn()
+        delay(1000)
+            .then(assertFunc)
+            .catch(err => {})
+
+        await null
+        expect(assertFunc).not.toHaveBeenCalled()
+
+        jest.runAllTimers()
+
+        await null
+        expect(assertFunc).toHaveBeenCalled()
+    })
+})