Stopwatch: Adds tests for TimerToggleButton

src/components/timerToggleButton/TimerToggleButton.test.js

@@ -0,0 +1,72 @@
+import React from 'react'
+import { fireEvent, render, screen } from '@testing-library/react';
+import TimerToggleButton from './TimerToggleButton';
+
+const stubSetElapsedTime = jest.fn();
+const stubSetIsRunning = jest.fn();
+const stubUseContext = jest.fn();
+
+const defaultContext = {
+    isRunning: false,
+    setElapsedTime: stubSetElapsedTime,
+    setIsRunning: stubSetIsRunning
+}
+
+const renderWithContext = (context = defaultContext) => {
+    React.useContext = stubUseContext.mockReturnValue(context)
+    return render(<TimerToggleButton/>)
+};
+
+beforeEach(() => {
+    jest.useFakeTimers();
+})
+
+afterEach(() => {
+    jest.useRealTimers();
+});
+
+test('should render as expected when isRunning is set to false', () => {
+const component = renderWithContext();
+
+    expect(component.container).toMatchSnapshot();
+});
+
+test('should render as expected when isRunning is set to true', () => {
+    const givenContext = {
+        ...defaultContext,
+        isRunning: true
+    }
+
+    const component = renderWithContext(givenContext);
+
+        expect(component.container).toMatchSnapshot();
+    });
+
+test('should call setIsRunning with true on button click when isRunning is false', () => {
+    renderWithContext();
+
+    const button = screen.getByText('Start');
+
+    fireEvent.click(button)
+
+    jest.runAllTimers();
+
+    expect(stubSetIsRunning).toHaveBeenCalledWith(true);
+});
+
+test('should call setIsRunning with false on button click when isRunning is true', () => {
+    const givenContext = {
+        ...defaultContext,
+        isRunning: true
+    }
+
+    renderWithContext(givenContext);
+
+    const button = screen.getByText('Stop');
+
+    fireEvent.click(button)
+
+    jest.runAllTimers();
+
+    expect(stubSetIsRunning).toHaveBeenCalledWith(false);
+});

src/components/timerToggleButton/__snapshots__/TimerToggleButton.test.js.snap

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+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`should render as expected when isRunning is set to false 1`] = `
+<div>
+  <button
+    class="button"
+    id="stopwatch-start-stop"
+  >
+    Start
+  </button>
+</div>
+`;
+
+exports[`should render as expected when isRunning is set to true 1`] = `
+<div>
+  <button
+    class="button"
+    id="stopwatch-start-stop"
+  >
+    Stop
+  </button>
+</div>
+`;