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Testing Core Utility Functions in Bootstrap

This test suite validates core utility functions in Bootstrap’s JavaScript codebase, including DOM manipulation, element state checking, and transition handling. It ensures reliable functionality of fundamental helper methods used throughout the framework.
Test Coverage Overview

The test suite provides comprehensive coverage of Bootstrap’s utility functions, including:
Element state validation (visibility, disabled status)
DOM element selection and manipulation
Transition and animation handling
jQuery integration and plugin management
Shadow DOM support and browser compatibility checks
Key edge cases around element visibility, disabled states, and transition timing are thoroughly tested.
Implementation Analysis

The tests utilize Jest’s describe/it structure with extensive use of spies and mocks to validate behavior. The implementation focuses on isolated unit testing of each utility function, with careful setup and teardown of DOM fixtures between tests. Browser-specific behavior is handled through feature detection and appropriate fallbacks.
Technical Details

Testing Framework: Jest
Test Helpers: Custom fixture management
DOM Manipulation: Native DOM APIs
Mocking: Jasmine spy functionality
Async Testing: Promise-based transition testing
Best Practices Demonstrated

The test suite exemplifies testing best practices including:
Proper test isolation and cleanup
Comprehensive edge case coverage
Async operation testing
Browser compatibility considerations
Clear test organization and naming
twbs/bootstrap

js/tests/unit/util/index.spec.js
            
import * as Util from '../../../src/util/index.js'
import { noop } from '../../../src/util/index.js'
import { clearFixture, getFixture } from '../../helpers/fixture.js'

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

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

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

  describe('getUID', () => {
    it('should generate uid', () => {
      const uid = Util.getUID('bs')
      const uid2 = Util.getUID('bs')

      expect(uid).not.toEqual(uid2)
    })
  })

  describe('getTransitionDurationFromElement', () => {
    it('should get transition from element', () => {
      fixtureEl.innerHTML = '<div style="transition: all 300ms ease-out;"></div>'

      expect(Util.getTransitionDurationFromElement(fixtureEl.querySelector('div'))).toEqual(300)
    })

    it('should return 0 if the element is undefined or null', () => {
      expect(Util.getTransitionDurationFromElement(null)).toEqual(0)
      expect(Util.getTransitionDurationFromElement(undefined)).toEqual(0)
    })

    it('should return 0 if the element do not possess transition', () => {
      fixtureEl.innerHTML = '<div></div>'

      expect(Util.getTransitionDurationFromElement(fixtureEl.querySelector('div'))).toEqual(0)
    })
  })

  describe('triggerTransitionEnd', () => {
    it('should trigger transitionend event', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div></div>'

        const el = fixtureEl.querySelector('div')
        const spy = spyOn(el, 'dispatchEvent').and.callThrough()

        el.addEventListener('transitionend', () => {
          expect(spy).toHaveBeenCalled()
          resolve()
        })

        Util.triggerTransitionEnd(el)
      })
    })
  })

  describe('isElement', () => {
    it('should detect if the parameter is an element or not and return Boolean', () => {
      fixtureEl.innerHTML = [
        '<div id="foo" class="test"></div>',
        '<div id="bar" class="test"></div>'
      ].join('')

      const el = fixtureEl.querySelector('#foo')

      expect(Util.isElement(el)).toBeTrue()
      expect(Util.isElement({})).toBeFalse()
      expect(Util.isElement(fixtureEl.querySelectorAll('.test'))).toBeFalse()
    })

    it('should detect jQuery element', () => {
      fixtureEl.innerHTML = '<div></div>'

      const el = fixtureEl.querySelector('div')
      const fakejQuery = {
        0: el,
        jquery: 'foo'
      }

      expect(Util.isElement(fakejQuery)).toBeTrue()
    })
  })

  describe('getElement', () => {
    it('should try to parse element', () => {
      fixtureEl.innerHTML = [
        '<div id="foo" class="test"></div>',
        '<div id="bar" class="test"></div>'
      ].join('')

      const el = fixtureEl.querySelector('div')

      expect(Util.getElement(el)).toEqual(el)
      expect(Util.getElement('#foo')).toEqual(el)
      expect(Util.getElement('#fail')).toBeNull()
      expect(Util.getElement({})).toBeNull()
      expect(Util.getElement([])).toBeNull()
      expect(Util.getElement()).toBeNull()
      expect(Util.getElement(null)).toBeNull()
      expect(Util.getElement(fixtureEl.querySelectorAll('.test'))).toBeNull()

      const fakejQueryObject = {
        0: el,
        jquery: 'foo'
      }

      expect(Util.getElement(fakejQueryObject)).toEqual(el)
    })
  })

  describe('isVisible', () => {
    it('should return false if the element is not defined', () => {
      expect(Util.isVisible(null)).toBeFalse()
      expect(Util.isVisible(undefined)).toBeFalse()
    })

    it('should return false if the element provided is not a dom element', () => {
      expect(Util.isVisible({})).toBeFalse()
    })

    it('should return false if the element is not visible with display none', () => {
      fixtureEl.innerHTML = '<div style="display: none;"></div>'

      const div = fixtureEl.querySelector('div')

      expect(Util.isVisible(div)).toBeFalse()
    })

    it('should return false if the element is not visible with visibility hidden', () => {
      fixtureEl.innerHTML = '<div style="visibility: hidden;"></div>'

      const div = fixtureEl.querySelector('div')

      expect(Util.isVisible(div)).toBeFalse()
    })

    it('should return false if an ancestor element is display none', () => {
      fixtureEl.innerHTML = [
        '<div style="display: none;">',
        '  <div>',
        '    <div>',
        '      <div class="content"></div>',
        '    </div>',
        '  </div>',
        '</div>'
      ].join('')

      const div = fixtureEl.querySelector('.content')

      expect(Util.isVisible(div)).toBeFalse()
    })

    it('should return false if an ancestor element is visibility hidden', () => {
      fixtureEl.innerHTML = [
        '<div style="visibility: hidden;">',
        '  <div>',
        '    <div>',
        '      <div class="content"></div>',
        '    </div>',
        '  </div>',
        '</div>'
      ].join('')

      const div = fixtureEl.querySelector('.content')

      expect(Util.isVisible(div)).toBeFalse()
    })

    it('should return true if an ancestor element is visibility hidden, but reverted', () => {
      fixtureEl.innerHTML = [
        '<div style="visibility: hidden;">',
        '  <div style="visibility: visible;">',
        '    <div>',
        '      <div class="content"></div>',
        '    </div>',
        '  </div>',
        '</div>'
      ].join('')

      const div = fixtureEl.querySelector('.content')

      expect(Util.isVisible(div)).toBeTrue()
    })

    it('should return true if the element is visible', () => {
      fixtureEl.innerHTML = [
        '<div>',
        '  <div id="element"></div>',
        '</div>'
      ].join('')

      const div = fixtureEl.querySelector('#element')

      expect(Util.isVisible(div)).toBeTrue()
    })

    it('should return false if the element is hidden, but not via display or visibility', () => {
      fixtureEl.innerHTML = [
        '<details>',
        '  <div id="element"></div>',
        '</details>'
      ].join('')

      const div = fixtureEl.querySelector('#element')

      expect(Util.isVisible(div)).toBeFalse()
    })

    it('should return true if its a closed details element', () => {
      fixtureEl.innerHTML = '<details id="element"></details>'

      const div = fixtureEl.querySelector('#element')

      expect(Util.isVisible(div)).toBeTrue()
    })

    it('should return true if the element is visible inside an open details element', () => {
      fixtureEl.innerHTML = [
        '<details open>',
        '  <div id="element"></div>',
        '</details>'
      ].join('')

      const div = fixtureEl.querySelector('#element')

      expect(Util.isVisible(div)).toBeTrue()
    })

    it('should return true if the element is a visible summary in a closed details element', () => {
      fixtureEl.innerHTML = [
        '<details>',
        '  <summary id="element-1">',
        '    <span id="element-2"></span>',
        '  </summary>',
        '</details>'
      ].join('')

      const element1 = fixtureEl.querySelector('#element-1')
      const element2 = fixtureEl.querySelector('#element-2')

      expect(Util.isVisible(element1)).toBeTrue()
      expect(Util.isVisible(element2)).toBeTrue()
    })
  })

  describe('isDisabled', () => {
    it('should return true if the element is not defined', () => {
      expect(Util.isDisabled(null)).toBeTrue()
      expect(Util.isDisabled(undefined)).toBeTrue()
      expect(Util.isDisabled()).toBeTrue()
    })

    it('should return true if the element provided is not a dom element', () => {
      expect(Util.isDisabled({})).toBeTrue()
      expect(Util.isDisabled('test')).toBeTrue()
    })

    it('should return true if the element has disabled attribute', () => {
      fixtureEl.innerHTML = [
        '<div>',
        '  <div id="element" disabled="disabled"></div>',
        '  <div id="element1" disabled="true"></div>',
        '  <div id="element2" disabled></div>',
        '</div>'
      ].join('')

      const div = fixtureEl.querySelector('#element')
      const div1 = fixtureEl.querySelector('#element1')
      const div2 = fixtureEl.querySelector('#element2')

      expect(Util.isDisabled(div)).toBeTrue()
      expect(Util.isDisabled(div1)).toBeTrue()
      expect(Util.isDisabled(div2)).toBeTrue()
    })

    it('should return false if the element has disabled attribute with "false" value, or doesn\'t have attribute', () => {
      fixtureEl.innerHTML = [
        '<div>',
        '  <div id="element" disabled="false"></div>',
        '  <div id="element1" ></div>',
        '</div>'
      ].join('')

      const div = fixtureEl.querySelector('#element')
      const div1 = fixtureEl.querySelector('#element1')

      expect(Util.isDisabled(div)).toBeFalse()
      expect(Util.isDisabled(div1)).toBeFalse()
    })

    it('should return false if the element is not disabled ', () => {
      fixtureEl.innerHTML = [
        '<div>',
        '  <button id="button"></button>',
        '  <select id="select"></select>',
        '  <select id="input"></select>',
        '</div>'
      ].join('')

      const el = selector => fixtureEl.querySelector(selector)

      expect(Util.isDisabled(el('#button'))).toBeFalse()
      expect(Util.isDisabled(el('#select'))).toBeFalse()
      expect(Util.isDisabled(el('#input'))).toBeFalse()
    })

    it('should return true if the element has disabled attribute', () => {
      fixtureEl.innerHTML = [
        '<div>',
        '  <input id="input" disabled="disabled">',
        '  <input id="input1" disabled="disabled">',
        '  <button id="button" disabled="true"></button>',
        '  <button id="button1" disabled="disabled"></button>',
        '  <button id="button2" disabled></button>',
        '  <select id="select" disabled></select>',
        '  <select id="input" disabled></select>',
        '</div>'
      ].join('')

      const el = selector => fixtureEl.querySelector(selector)

      expect(Util.isDisabled(el('#input'))).toBeTrue()
      expect(Util.isDisabled(el('#input1'))).toBeTrue()
      expect(Util.isDisabled(el('#button'))).toBeTrue()
      expect(Util.isDisabled(el('#button1'))).toBeTrue()
      expect(Util.isDisabled(el('#button2'))).toBeTrue()
      expect(Util.isDisabled(el('#input'))).toBeTrue()
    })

    it('should return true if the element has class "disabled"', () => {
      fixtureEl.innerHTML = [
        '<div>',
        '  <div id="element" class="disabled"></div>',
        '</div>'
      ].join('')

      const div = fixtureEl.querySelector('#element')

      expect(Util.isDisabled(div)).toBeTrue()
    })

    it('should return true if the element has class "disabled" but disabled attribute is false', () => {
      fixtureEl.innerHTML = [
        '<div>',
        '  <input id="input" class="disabled" disabled="false">',
        '</div>'
      ].join('')

      const div = fixtureEl.querySelector('#input')

      expect(Util.isDisabled(div)).toBeTrue()
    })
  })

  describe('findShadowRoot', () => {
    it('should return null if shadow dom is not available', () => {
      // Only for newer browsers
      if (!document.documentElement.attachShadow) {
        expect().nothing()
        return
      }

      fixtureEl.innerHTML = '<div></div>'

      const div = fixtureEl.querySelector('div')

      spyOn(document.documentElement, 'attachShadow').and.returnValue(null)

      expect(Util.findShadowRoot(div)).toBeNull()
    })

    it('should return null when we do not find a shadow root', () => {
      // Only for newer browsers
      if (!document.documentElement.attachShadow) {
        expect().nothing()
        return
      }

      spyOn(document, 'getRootNode').and.returnValue(undefined)

      expect(Util.findShadowRoot(document)).toBeNull()
    })

    it('should return the shadow root when found', () => {
      // Only for newer browsers
      if (!document.documentElement.attachShadow) {
        expect().nothing()
        return
      }

      fixtureEl.innerHTML = '<div></div>'

      const div = fixtureEl.querySelector('div')
      const shadowRoot = div.attachShadow({
        mode: 'open'
      })

      expect(Util.findShadowRoot(shadowRoot)).toEqual(shadowRoot)

      shadowRoot.innerHTML = '<button>Shadow Button</button>'

      expect(Util.findShadowRoot(shadowRoot.firstChild)).toEqual(shadowRoot)
    })
  })

  describe('noop', () => {
    it('should be a function', () => {
      expect(Util.noop).toEqual(jasmine.any(Function))
    })
  })

  describe('reflow', () => {
    it('should return element offset height to force the reflow', () => {
      fixtureEl.innerHTML = '<div></div>'

      const div = fixtureEl.querySelector('div')
      const spy = spyOnProperty(div, 'offsetHeight')
      Util.reflow(div)
      expect(spy).toHaveBeenCalled()
    })
  })

  describe('getjQuery', () => {
    const fakejQuery = { trigger() {} }

    beforeEach(() => {
      Object.defineProperty(window, 'jQuery', {
        value: fakejQuery,
        writable: true
      })
    })

    afterEach(() => {
      window.jQuery = undefined
    })

    it('should return jQuery object when present', () => {
      expect(Util.getjQuery()).toEqual(fakejQuery)
    })

    it('should not return jQuery object when present if data-bs-no-jquery', () => {
      document.body.setAttribute('data-bs-no-jquery', '')

      expect(window.jQuery).toEqual(fakejQuery)
      expect(Util.getjQuery()).toBeNull()

      document.body.removeAttribute('data-bs-no-jquery')
    })

    it('should not return jQuery if not present', () => {
      window.jQuery = undefined
      expect(Util.getjQuery()).toBeNull()
    })
  })

  describe('onDOMContentLoaded', () => {
    it('should execute callbacks when DOMContentLoaded is fired and should not add more than one listener', () => {
      const spy = jasmine.createSpy()
      const spy2 = jasmine.createSpy()

      const spyAdd = spyOn(document, 'addEventListener').and.callThrough()
      spyOnProperty(document, 'readyState').and.returnValue('loading')

      Util.onDOMContentLoaded(spy)
      Util.onDOMContentLoaded(spy2)

      document.dispatchEvent(new Event('DOMContentLoaded', {
        bubbles: true,
        cancelable: true
      }))

      expect(spy).toHaveBeenCalled()
      expect(spy2).toHaveBeenCalled()
      expect(spyAdd).toHaveBeenCalledTimes(1)
    })

    it('should execute callback if readyState is not "loading"', () => {
      const spy = jasmine.createSpy()
      Util.onDOMContentLoaded(spy)
      expect(spy).toHaveBeenCalled()
    })
  })

  describe('defineJQueryPlugin', () => {
    const fakejQuery = { fn: {} }

    beforeEach(() => {
      Object.defineProperty(window, 'jQuery', {
        value: fakejQuery,
        writable: true
      })
    })

    afterEach(() => {
      window.jQuery = undefined
    })

    it('should define a plugin on the jQuery instance', () => {
      const pluginMock = Util.noop
      pluginMock.NAME = 'test'
      pluginMock.jQueryInterface = Util.noop

      Util.defineJQueryPlugin(pluginMock)
      expect(fakejQuery.fn.test).toEqual(pluginMock.jQueryInterface)
      expect(fakejQuery.fn.test.Constructor).toEqual(pluginMock)
      expect(fakejQuery.fn.test.noConflict).toEqual(jasmine.any(Function))
    })
  })

  describe('execute', () => {
    it('should execute if arg is function', () => {
      const spy = jasmine.createSpy('spy')
      Util.execute(spy)
      expect(spy).toHaveBeenCalled()
    })

    it('should execute if arg is function & return the result', () => {
      const functionFoo = (num1, num2 = 10) => num1 + num2
      const resultFoo = Util.execute(functionFoo, [undefined, 4, 5])
      expect(resultFoo).toBe(9)

      const resultFoo1 = Util.execute(functionFoo, [undefined, 4])
      expect(resultFoo1).toBe(14)

      const functionBar = () => 'foo'
      const resultBar = Util.execute(functionBar)
      expect(resultBar).toBe('foo')
    })

    it('should not execute if arg is not function & return default argument', () => {
      const foo = 'bar'
      expect(Util.execute(foo)).toBe('bar')
      expect(Util.execute(foo, [], 4)).toBe(4)
    })
  })

  describe('executeAfterTransition', () => {
    it('should immediately execute a function when waitForTransition parameter is false', () => {
      const el = document.createElement('div')
      const callbackSpy = jasmine.createSpy('callback spy')
      const eventListenerSpy = spyOn(el, 'addEventListener')

      Util.executeAfterTransition(callbackSpy, el, false)

      expect(callbackSpy).toHaveBeenCalled()
      expect(eventListenerSpy).not.toHaveBeenCalled()
    })

    it('should execute a function when a transitionend event is dispatched', () => {
      const el = document.createElement('div')
      const callbackSpy = jasmine.createSpy('callback spy')

      spyOn(window, 'getComputedStyle').and.returnValue({
        transitionDuration: '0.05s',
        transitionDelay: '0s'
      })

      Util.executeAfterTransition(callbackSpy, el)

      el.dispatchEvent(new TransitionEvent('transitionend'))

      expect(callbackSpy).toHaveBeenCalled()
    })

    it('should execute a function after a computed CSS transition duration and there was no transitionend event dispatched', () => {
      return new Promise(resolve => {
        const el = document.createElement('div')
        const callbackSpy = jasmine.createSpy('callback spy')

        spyOn(window, 'getComputedStyle').and.returnValue({
          transitionDuration: '0.05s',
          transitionDelay: '0s'
        })

        Util.executeAfterTransition(callbackSpy, el)

        setTimeout(() => {
          expect(callbackSpy).toHaveBeenCalled()
          resolve()
        }, 70)
      })
    })

    it('should not execute a function a second time after a computed CSS transition duration and if a transitionend event has already been dispatched', () => {
      return new Promise(resolve => {
        const el = document.createElement('div')
        const callbackSpy = jasmine.createSpy('callback spy')

        spyOn(window, 'getComputedStyle').and.returnValue({
          transitionDuration: '0.05s',
          transitionDelay: '0s'
        })

        Util.executeAfterTransition(callbackSpy, el)

        setTimeout(() => {
          el.dispatchEvent(new TransitionEvent('transitionend'))
        }, 50)

        setTimeout(() => {
          expect(callbackSpy).toHaveBeenCalledTimes(1)
          resolve()
        }, 70)
      })
    })

    it('should not trigger a transitionend event if another transitionend event had already happened', () => {
      return new Promise(resolve => {
        const el = document.createElement('div')

        spyOn(window, 'getComputedStyle').and.returnValue({
          transitionDuration: '0.05s',
          transitionDelay: '0s'
        })

        Util.executeAfterTransition(noop, el)

        // simulate a event dispatched by the browser
        el.dispatchEvent(new TransitionEvent('transitionend'))

        const dispatchSpy = spyOn(el, 'dispatchEvent').and.callThrough()

        setTimeout(() => {
          // setTimeout should not have triggered another transitionend event.
          expect(dispatchSpy).not.toHaveBeenCalled()
          resolve()
        }, 70)
      })
    })

    it('should ignore transitionend events from nested elements', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = [
          '<div class="outer">',
          '  <div class="nested"></div>',
          '</div>'
        ].join('')

        const outer = fixtureEl.querySelector('.outer')
        const nested = fixtureEl.querySelector('.nested')
        const callbackSpy = jasmine.createSpy('callback spy')

        spyOn(window, 'getComputedStyle').and.returnValue({
          transitionDuration: '0.05s',
          transitionDelay: '0s'
        })

        Util.executeAfterTransition(callbackSpy, outer)

        nested.dispatchEvent(new TransitionEvent('transitionend', {
          bubbles: true
        }))

        setTimeout(() => {
          expect(callbackSpy).not.toHaveBeenCalled()
        }, 20)

        setTimeout(() => {
          expect(callbackSpy).toHaveBeenCalled()
          resolve()
        }, 70)
      })
    })
  })

  describe('getNextActiveElement', () => {
    it('should return first element if active not exists or not given and shouldGetNext is either true, or false with cycling being disabled', () => {
      const array = ['a', 'b', 'c', 'd']

      expect(Util.getNextActiveElement(array, '', true, true)).toEqual('a')
      expect(Util.getNextActiveElement(array, 'g', true, true)).toEqual('a')
      expect(Util.getNextActiveElement(array, '', true, false)).toEqual('a')
      expect(Util.getNextActiveElement(array, 'g', true, false)).toEqual('a')
      expect(Util.getNextActiveElement(array, '', false, false)).toEqual('a')
      expect(Util.getNextActiveElement(array, 'g', false, false)).toEqual('a')
    })

    it('should return last element if active not exists or not given and shouldGetNext is false but cycling is enabled', () => {
      const array = ['a', 'b', 'c', 'd']

      expect(Util.getNextActiveElement(array, '', false, true)).toEqual('d')
      expect(Util.getNextActiveElement(array, 'g', false, true)).toEqual('d')
    })

    it('should return next element or same if is last', () => {
      const array = ['a', 'b', 'c', 'd']

      expect(Util.getNextActiveElement(array, 'a', true, true)).toEqual('b')
      expect(Util.getNextActiveElement(array, 'b', true, true)).toEqual('c')
      expect(Util.getNextActiveElement(array, 'd', true, false)).toEqual('d')
    })

    it('should return next element or first, if is last and "isCycleAllowed = true"', () => {
      const array = ['a', 'b', 'c', 'd']

      expect(Util.getNextActiveElement(array, 'c', true, true)).toEqual('d')
      expect(Util.getNextActiveElement(array, 'd', true, true)).toEqual('a')
    })

    it('should return previous element or same if is first', () => {
      const array = ['a', 'b', 'c', 'd']

      expect(Util.getNextActiveElement(array, 'b', false, true)).toEqual('a')
      expect(Util.getNextActiveElement(array, 'd', false, true)).toEqual('c')
      expect(Util.getNextActiveElement(array, 'a', false, false)).toEqual('a')
    })

    it('should return next element or first, if is last and "isCycleAllowed = true"', () => {
      const array = ['a', 'b', 'c', 'd']

      expect(Util.getNextActiveElement(array, 'd', false, true)).toEqual('c')
      expect(Util.getNextActiveElement(array, 'a', false, true)).toEqual('d')
    })
  })
})