Adding upstream version 5.2.3+dfsg.

Signed-off-by: Daniel Baumann <daniel@debian.org>

js/tests/README.md

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+## How does Bootstrap's test suite work?
+
+Bootstrap uses [Jasmine](https://jasmine.github.io/). 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](https://karma-runner.github.io/), run `npm run js-test`.
+To run the unit test suite via [Karma](https://karma-runner.github.io/) 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](https://jasmine.github.io/pages/docs_home.html) 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`](https://jasmine.github.io/api/edge/matchers.html) to ensure something is expected.
+- Each test should follow the project's [JavaScript Code Guidelines](https://github.com/twbs/bootstrap/blob/main/.github/CONTRIBUTING.md#js)
+
+## 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
+
+```js
+// Synchronous test
+describe('getInstance', () => {
+  it('should return null if there is no instance', () => {
+    // Make assertion
+    expect(Tab.getInstance(fixtureEl)).toBeNull()
+  })
+
+  it('should return this instance', () => {
+    fixtureEl.innerHTML = '<div></div>'
+
+    const divEl = fixtureEl.querySelector('div')
+    const tab = new Tab(divEl)
+
+    // Make assertion
+    expect(Tab.getInstance(divEl)).toEqual(tab)
+  })
+})
+
+// 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('shown.bs.tooltip', () => {
+      const tip = document.querySelector('.tooltip')
+
+      expect(tip).not.toBeNull()
+      expect(tip.classList.contains('fade')).toEqual(false)
+      resolve()
+    })
+
+    tooltip.show()
+  })
+})
+```