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Testing Alert Component Implementation in Bootstrap

This test suite validates the Alert component functionality in Bootstrap, covering initialization, data-api interactions, and lifecycle methods. The tests ensure proper alert creation, dismissal, and jQuery integration.

Test Coverage Overview

The test suite provides comprehensive coverage of the Alert component’s core functionality.

Element initialization via CSS selectors and DOM elements
Data-API driven alert dismissal
Alert closing behavior with and without transitions
Event prevention handling
Instance management and disposal

Implementation Analysis

The testing approach utilizes Jest’s describe/it blocks for organized test grouping. The implementation leverages fixture-based testing with beforeAll/afterEach hooks for consistent test environment setup. Promises are used to handle asynchronous transition testing, with careful attention to event handling and state verification.

Technical Details

Testing Framework: Jest
Fixture Helpers: clearFixture, getFixture
Mock Utilities: jQueryMock
Event Simulation: click events, transition events
Instance Management: getInstance, getOrCreateInstance methods

Best Practices Demonstrated

The test suite exemplifies several testing best practices including isolated test cases, proper setup/teardown patterns, and comprehensive edge case coverage.

Consistent fixture cleanup between tests
Async testing with Promises
Error case validation
Protected method access verification
Instance lifecycle management

twbs/bootstrap

js/tests/unit/alert.spec.js

            
import Alert from '../../src/alert.js'
import { getTransitionDurationFromElement } from '../../src/util/index.js'
import { clearFixture, getFixture, jQueryMock } from '../helpers/fixture.js'

describe('Alert', () => {
  let fixtureEl

  beforeAll(() => {
    fixtureEl = getFixture()
  })

  afterEach(() => {
    clearFixture()
  })

  it('should take care of element either passed as a CSS selector or DOM element', () => {
    fixtureEl.innerHTML = '<div class="alert"></div>'

    const alertEl = fixtureEl.querySelector('.alert')
    const alertBySelector = new Alert('.alert')
    const alertByElement = new Alert(alertEl)

    expect(alertBySelector._element).toEqual(alertEl)
    expect(alertByElement._element).toEqual(alertEl)
  })

  it('should return version', () => {
    expect(Alert.VERSION).toEqual(jasmine.any(String))
  })

  describe('DATA_KEY', () => {
    it('should return plugin data key', () => {
      expect(Alert.DATA_KEY).toEqual('bs.alert')
    })
  })

  describe('data-api', () => {
    it('should close an alert without instantiating it manually', () => {
      fixtureEl.innerHTML = [
        '<div class="alert">',
        '  <button type="button" data-bs-dismiss="alert">x</button>',
        '</div>'
      ].join('')

      const button = document.querySelector('button')

      button.click()
      expect(document.querySelectorAll('.alert')).toHaveSize(0)
    })

    it('should close an alert without instantiating it manually with the parent selector', () => {
      fixtureEl.innerHTML = [
        '<div class="alert">',
        '  <button type="button" data-bs-target=".alert" data-bs-dismiss="alert">x</button>',
        '</div>'
      ].join('')

      const button = document.querySelector('button')

      button.click()
      expect(document.querySelectorAll('.alert')).toHaveSize(0)
    })
  })

  describe('close', () => {
    it('should close an alert', () => {
      return new Promise(resolve => {
        const spy = jasmine.createSpy('spy', getTransitionDurationFromElement)
        fixtureEl.innerHTML = '<div class="alert"></div>'

        const alertEl = document.querySelector('.alert')
        const alert = new Alert(alertEl)

        alertEl.addEventListener('closed.bs.alert', () => {
          expect(document.querySelectorAll('.alert')).toHaveSize(0)
          expect(spy).not.toHaveBeenCalled()
          resolve()
        })

        alert.close()
      })
    })

    it('should close alert with fade class', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div class="alert fade"></div>'

        const alertEl = document.querySelector('.alert')
        const alert = new Alert(alertEl)

        alertEl.addEventListener('transitionend', () => {
          expect().nothing()
        })

        alertEl.addEventListener('closed.bs.alert', () => {
          expect(document.querySelectorAll('.alert')).toHaveSize(0)
          resolve()
        })

        alert.close()
      })
    })

    it('should not remove alert if close event is prevented', () => {
      return new Promise((resolve, reject) => {
        fixtureEl.innerHTML = '<div class="alert"></div>'

        const getAlert = () => document.querySelector('.alert')
        const alertEl = getAlert()
        const alert = new Alert(alertEl)

        alertEl.addEventListener('close.bs.alert', event => {
          event.preventDefault()
          setTimeout(() => {
            expect(getAlert()).not.toBeNull()
            resolve()
          }, 10)
        })

        alertEl.addEventListener('closed.bs.alert', () => {
          reject(new Error('should not fire closed event'))
        })

        alert.close()
      })
    })
  })

  describe('dispose', () => {
    it('should dispose an alert', () => {
      fixtureEl.innerHTML = '<div class="alert"></div>'

      const alertEl = document.querySelector('.alert')
      const alert = new Alert(alertEl)

      expect(Alert.getInstance(alertEl)).not.toBeNull()

      alert.dispose()

      expect(Alert.getInstance(alertEl)).toBeNull()
    })
  })

  describe('jQueryInterface', () => {
    it('should handle config passed and toggle existing alert', () => {
      fixtureEl.innerHTML = '<div class="alert"></div>'

      const alertEl = fixtureEl.querySelector('.alert')
      const alert = new Alert(alertEl)

      const spy = spyOn(alert, 'close')

      jQueryMock.fn.alert = Alert.jQueryInterface
      jQueryMock.elements = [alertEl]

      jQueryMock.fn.alert.call(jQueryMock, 'close')

      expect(spy).toHaveBeenCalled()
    })

    it('should create new alert instance and call close', () => {
      fixtureEl.innerHTML = '<div class="alert"></div>'

      const alertEl = fixtureEl.querySelector('.alert')

      jQueryMock.fn.alert = Alert.jQueryInterface
      jQueryMock.elements = [alertEl]

      expect(Alert.getInstance(alertEl)).toBeNull()
      jQueryMock.fn.alert.call(jQueryMock, 'close')

      expect(fixtureEl.querySelector('.alert')).toBeNull()
    })

    it('should just create an alert instance without calling close', () => {
      fixtureEl.innerHTML = '<div class="alert"></div>'

      const alertEl = fixtureEl.querySelector('.alert')

      jQueryMock.fn.alert = Alert.jQueryInterface
      jQueryMock.elements = [alertEl]

      jQueryMock.fn.alert.call(jQueryMock)

      expect(Alert.getInstance(alertEl)).not.toBeNull()
      expect(fixtureEl.querySelector('.alert')).not.toBeNull()
    })

    it('should throw an error on undefined method', () => {
      fixtureEl.innerHTML = '<div></div>'

      const div = fixtureEl.querySelector('div')
      const action = 'undefinedMethod'

      jQueryMock.fn.alert = Alert.jQueryInterface
      jQueryMock.elements = [div]

      expect(() => {
        jQueryMock.fn.alert.call(jQueryMock, action)
      }).toThrowError(TypeError, `No method named "${action}"`)
    })

    it('should throw an error on protected method', () => {
      fixtureEl.innerHTML = '<div></div>'

      const div = fixtureEl.querySelector('div')
      const action = '_getConfig'

      jQueryMock.fn.alert = Alert.jQueryInterface
      jQueryMock.elements = [div]

      expect(() => {
        jQueryMock.fn.alert.call(jQueryMock, action)
      }).toThrowError(TypeError, `No method named "${action}"`)
    })
  })

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

      const div = fixtureEl.querySelector('div')
      const alert = new Alert(div)

      expect(Alert.getInstance(div)).toEqual(alert)
      expect(Alert.getInstance(div)).toBeInstanceOf(Alert)
    })

    it('should return null when there is no alert instance', () => {
      fixtureEl.innerHTML = '<div></div>'

      const div = fixtureEl.querySelector('div')

      expect(Alert.getInstance(div)).toBeNull()
    })
  })

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

      const div = fixtureEl.querySelector('div')
      const alert = new Alert(div)

      expect(Alert.getOrCreateInstance(div)).toEqual(alert)
      expect(Alert.getInstance(div)).toEqual(Alert.getOrCreateInstance(div, {}))
      expect(Alert.getOrCreateInstance(div)).toBeInstanceOf(Alert)
    })

    it('should return new instance when there is no alert instance', () => {
      fixtureEl.innerHTML = '<div></div>'

      const div = fixtureEl.querySelector('div')

      expect(Alert.getInstance(div)).toBeNull()
      expect(Alert.getOrCreateInstance(div)).toBeInstanceOf(Alert)
    })
  })
})