#31 : Add unit tests

src/utils/interval.test.js

@@ -0,0 +1,30 @@
+import {
+  setIntervalImmediate,
+} from './interval.js'
+
+describe('setIntervalImmediate', () => {
+  beforeEach(() => {
+    jest.useFakeTimers();
+  })
+
+  it('runs callback immediately and them each n ms', () => {
+    let interval
+    const durationMs = 1000
+
+    const callNumbersToStopTimer = 3
+    let calledTimes = 0
+    const callback = () => {
+      calledTimes++
+      if (calledTimes === callNumbersToStopTimer) {
+        clearInterval(interval)
+      }
+    }
+
+    interval = setIntervalImmediate(callback, durationMs)
+    jest.runAllTimers()
+
+    expect(calledTimes).toBe(callNumbersToStopTimer)
+    expect(setInterval).toHaveBeenCalledWith(expect.any(Function), durationMs)
+    expect(clearInterval).toHaveBeenCalledWith(interval)
+  })
+})