@wwtdev/bsds-components v1.16.5

BSDS Components Core Package

This is the core dependency for our framework-compatible packages:

• @wwtdev/bsds-components-vue2
• @wwtdev/bsds-components-vue3

Component & Unit Testing

The following packages have been installed for component / unit testing:

• Stencil Core Testing - Testing library included with Stencil.
• Jest - JavaScript testing framework.
• @testing-library/dom - DOM Testing Library which provides various utilities for querying the DOM.
• Faker - Helps generate fake (but realistic) data for testing.

Component vs Unit Tests

There are a couple key differences between Component and Unit testing. For the majority of this component library, we will be writing Component tests. The Vue documentation site actually does a very good job of explaining the differences (Unit Testing vs Component Testing), however, here are some key differences for quick reference:

Unit Testing

These should primarily test isolated "units" of business code (functions, composable, etc.). Typically written for utility functions, custom hooks, or composables, but not actual Web components.

Component Testing

These tests focus on a component's props, events, slots, styles, classes, hooks, etc. Primarily write tests which set/update props, fire events, etc. which should update the presentation of the component. Then, check the outputted component code.

Run Unit Tests

Runs the full unit test suite.

npm run test

Watch Unit Tests

Runs and watches for changes on the full unit test suite.

npm run test:watch

Run Unit Tests with Coverage

Runs the full unit test suite and outputs a coverage report. This report can be seen both in the console output and as an HTML page at coverage/lcov-report/index.html.

npm run test:coverage

Run Specific Unit Test(s)

There's a slight issue with Stencil v2.13.0 that won't let Jest CLI arguments pass through properly, so these instructions will change when/if our Stencil version is upgraded.

Add -- t [test name pattern] to any test command (except coverage) to run for a particular file pattern.

• npm run test -- t [test name pattern]
• npm run test:watch -- t [test name pattern]

For coverage, just add -- [test name pattern].

• npm run test:coverage -- [test name pattern]

Examples:

• npm run test -- t bs-button.spec.tsx runs just bs-button.spec.tsx.
• npm run test:watch -- t bs-banner runs just bs-banner.spec.tsx and watches for changes.
• npm run test -- t profile runs all tests with "profile" in the name .(bs-profile-img.spec.tsx, bs-profile-layout.spec.tsx, bs-profile.spec.tsx, bs-profile-details.spec.tsx).
• npm run test:coverage -- bs-banner runs coverage report for bs-banner.spec.tsx.

Testing Tips & Tricks

Test Structure

• Suggest using the describe() function from Jest to structure the test in a meaningful way. For example, an overall describe('Component Tests') for containing all the tests then another describe('functionName()') for each function.
• it() from Jest should be used to describe the test input/output. For example, it('should do this when this and that are set').
• beforeEach() and afterEach() can be used for setting up/cleaning up everything within a describe() section.

Mounting for Component Tests

• Mount components using newSpecPage(). For example:

const page = await newSpecPage({
  components: [BsBadge],
  html: `<bs-badge color="blue">Some Content</bs-badge>`,
});

• const component = page.root; to get the root component.
• Components can be queried like any HTML element. For example:

const component = page.root.querySelector('.bs-toast') as HTMLElement;

expect(component.getAttribute('data-shown')).toBe('');

• Dynamically updating props/state values is possible by using page.rootInstance. For example, updating the isVisible state can be done by page.rootInstance.isVisible = true.
• await page.waitForChanges() for waiting for state / props updates to propagate.

What to Test

• Primarily test rendered component for various things such as attributes, slot content, event handling, etc.
  • Test an attribute: expect(component.getAttribute('data-shown')).toBe('Some Val');.
  • Test text content: expect(component.textContent).toBe('Some Text');.
• Testing prop values being placed on the DOM adds no real value unless those values are dynamically shown. For example, :data-text="textBtn ? '' : undefined". In this example we would write two tests. One for each branch of the condition.
• Make sure to hit as many branches as possible, edge cases, etc. in other component logic. Check coverage report to see what may be missed.
• Also consider that sometimes a test would not add any meaningful value. For example, writing a unit test for a getter. While this would improve coverage numbers, the test itself adds no value.

Event Testing

• @testing-library/dom adds a very useful function for testing events: fireEvent.
• Here's a sample usage a Jest mock and firing an event to test something:

const evMock = jest.fn();
element.addEventListener('mouseenter', evMock);

fireEvent.mouseEnter(page.root);

expect(evMock).toHaveBeenCalled();

• Firing a custom event:

const ev = new CustomEvent('oncustomname', { detail: 'some event detail' })
fireEvent(page.root, ev)

Miscellaneous Tips

• Use faker from @faker-js/faker to create realistic test data.
• Jest provides various ways to handle faking timers if a component uses setTimeout(). Be sure to jest.clearAllTimers() after each test since this can mess with the async component mounting.

// Fake-out the timer system for these tests so it's more predictable
beforeEach(() => jest.useFakeTimers());

// Clean up timers in the system
afterEach(() => jest.clearAllTimers());

it('should test some timer features', () => {
  // mount and do some updates to trigger the timer
  jest.advanceTimersByTime(300);
  // expect something to have happened
});

• jest.useFakeTimers() will not work when a test itself is async (e.g. it('should test something', async () => { // test })). In this case, here are a couple ways to test async code:
  • One-liner using Promise which waits for a 500ms timer:

      it('should run some async code', async () => {
        ...
        // trigger code here
        ...
        // wait 500ms
        await new Promise(res => setTimeout(res, 500))
        ...
        // expect some result here
        expect('actual').toBe('expected')
      })

  • Using a done argument to the test case which tells the test when it is finished:

      it('should run some async code', async (done) => {
        ...
        // trigger code here
        ...
        setTimeout(() => {
          // expect some result after 500ms
          expect('actual').toBe('expected')
          ...
          // call done when finished
          done()
        }, 500)
      })