How does Bootstrap’s test suite work?

Bootstrap uses Jasmine. Each plugin has a file dedicated to its tests in tests/unit/<plugin-name>.spec.js.

  • visual/ contains “visual” tests which are run interactively in real browsers and require manual verification by humans.

To run the unit test suite via Karma, run npm run js-test. To run the unit test suite via Karma and debug, run npm run js-debug.

How do I add a new unit test?

  1. Locate and open the file dedicated to the plugin which you need to add tests to (tests/unit/<plugin-name>.spec.js).
  2. Review the Jasmine API Documentation and use the existing tests as references for how to structure your new tests.
  3. Write the necessary unit test(s) for the new or revised functionality.
  4. Run npm run js-test to see the results of your newly-added test(s).

Note: Your new unit tests should fail before your changes are applied to the plugin, and should pass after your changes are applied to the plugin.

What should a unit test look like?

  • Each test should have a unique name clearly stating what unit is being tested.
  • Each test should be in the corresponding describe.
  • Each test should test only one unit per test, although one test can include several assertions. Create multiple tests for multiple units of functionality.
  • Each test should use expect to ensure something is expected.
  • Each test should follow the project’s JavaScript Code Guidelines

Code coverage

Currently we’re aiming for at least 90% test coverage for our code. To ensure your changes meet or exceed this limit, run npm run js-test-karma and open the file in js/coverage/lcov-report/index.html to see the code coverage for each plugin. See more details when you select a plugin and ensure your change is fully covered by unit tests.

Example tests

// Synchronous test
describe('getInstance', () => {
  it('should return null if there is no instance', () => {
    // Make assertion

  it('should return this instance', () => {
    fixtureEl.innerHTML = '<div></div>'

    const divEl = fixtureEl.querySelector('div')
    const tab = new Tab(divEl)

    // Make assertion

// Asynchronous test
it('should show a tooltip without the animation', () => {
  return new Promise(resolve => {
    fixtureEl.innerHTML = '<a href="#" rel="tooltip" title="Another tooltip"></a>'

    const tooltipEl = fixtureEl.querySelector('a')
    const tooltip = new Tooltip(tooltipEl, {
      animation: false

    tooltipEl.addEventListener('', () => {
      const tip = document.querySelector('.tooltip')