moved up to 5

step2-04/demo/README.md

@@ -0,0 +1,128 @@
+# Step 2.4: Testing TypeScript code with Jest (Demo)
+
+[Lessons](../) | [Exercise](./exercise/) | [Demo](./demo/)
+
+[Jest](https://jestjs.io/) is a test framework made by Facebook and is very popular in the React and wider JS ecosystems.
+
+In this exercise, we will work on implementing simple unit tests using Jest.
+
+## Jest Features
+
+- Multi-threaded and isolated test runner
+- Provides a fake browser-like environment if needed (window, document, DOM, etc) using jsdom
+- Snapshots: Jest can create text-based snapshots of rendered components. These snapshots can be checked in and show API or large object changes alongside code changes in pull requests.
+- Code coverage is integrated (`--coverage`)
+- Very clear error messages showing where a test failure occurred
+
+## How to use Jest
+
+- Using `create-react-app` or other project generators, Jest should already be pre-configured. Running `npm test` usually will trigger it!
+- A `jest.config.js` file is used for configuration
+- `jsdom` might not have enough API from real browsers, for those cases, polyfills are required. Place these inside `jest.setup.js` and hook up the setup file in `jest.config.js`
+- in order to use `enzyme` library to test React Components, more config bits are needed inside `jest.setup.js`
+
+## What does a test look like?
+
+```ts
+// describe(), it() and expect() are globally exported, so they don't need to be imported when jest runs these tests
+describe('Something to be tested', () => {
+  it('should describe the behavior', () => {
+    expect(true).toBe(true);
+  });
+});
+```
+
+## Testing React components using Enzyme
+
+[Enzyme](https://airbnb.io/enzyme/) is made by Airbnb and provides utilities to help test React components.
+
+In a real app using ReactDOM, the top-level component will be rendered on the page using `ReactDOM.render()`. Enzyme provides a lighter-weight `mount()` function which is usually adequate for testing purposes.
+
+`mount()` returns a wrapper that can be inspected and provides functionality like `find()`, simulating clicks, etc.
+
+The following code demonstrates how Enzyme can be used to help test React components.
+
+```tsx
+import React from 'react';
+import { mount } from 'enzyme';
+import { TestMe } from './TestMe';
+
+describe('TestMe Component', () => {
+  it('should have a non-clickable component when the original InnerMe is clicked', () => {
+    const wrapper = mount(<TestMe name="world" />);
+    wrapper.find('#innerMe').simulate('click');
+    expect(wrapper.find('#innerMe').text()).toBe('Clicked');
+  });
+});
+
+describe('Foo Component Tests', () => {
+  it('allows us to set props', () => {
+    const wrapper = mount(<Foo bar="baz" />);
+    expect(wrapper.props().bar).toBe('baz');
+    wrapper.setProps({ bar: 'foo' });
+    expect(wrapper.props().bar).toBe('foo');
+
+    wrapper.find('button').simulate('click');
+  });
+});
+```
+
+## Advanced topics
+
+### Mocking
+
+Mocking functions is a large part of what makes Jest a powerful testing library. Jest actually intercepts the module loading process in Node.js, allowing it to mock entire modules if needed.
+
+There are many ways to mock, as you'd imagine in a language as flexible as JS. We only look at the simplest case, but there's a lot of depth here.
+
+To mock a function:
+
+```ts
+it('some test function', () => {
+  const mockCallback = jest.fn(x => 42 + x);
+  mockCallback(1);
+  mockCallback(2);
+  expect(mockCallback).toHaveBeenCalledTimes(2);
+});
+```
+
+Read more about jest mocking [here](https://jestjs.io/docs/en/mock-functions.html).
+
+### Async Testing
+
+For testing async scenarios, the test runner needs some way to know when the scenario is finished. Jest tests can handle async scenarios using callbacks, promises, or async/await.
+
+```ts
+// Callback
+it('tests callback functions', (done) => {
+  setTimeout(() => {
+    done();
+  }, 1000);
+});
+
+// Returning a promise
+it('tests promise functions', () => {
+  return someFunctionThatReturnsPromise());
+});
+
+// Async/await (recommended)
+it('tests async functions', async () => {
+  expect(await someFunction()).toBe(5);
+});
+```
+
+# Demo
+
+## Jest basics
+
+In this repo, we can start an inner loop development of tests by running `npm test` from the root of the `frontend-bootcamp` folder.
+
+Take a look at code inside `demo/src`:
+
+1. `index.ts` exports a few functions for a counter as well as a function for squaring numbers. We'll use this last function to demonstrate how mocks work.
+
+2. `multiply.ts` is a contrived example of a function that is exported
+
+3. `index.spec.ts` is the test file
+
+Note how tests are re-run when either test files or source files under `src` are saved.

step2-04/demo/index.html

@@ -4,7 +4,7 @@
     <link rel="stylesheet" href="../../assets/step.css" />
   </head>
   <body class="ms-Fabric">
-    <div id="markdownReadme"></div>
+    <div id="markdownReadme" data-src="./README.md"></div>
     <div id="app">
       For this step, we look at unit testing. Run
       <pre>npm test</pre>