{"id":1660,"date":"2017-08-05T22:00:00","date_gmt":"2017-08-05T20:00:00","guid":{"rendered":"https:\/\/demo.sidekick.be\/itenium\/javascript-testing-jasmine-customization\/"},"modified":"2025-11-28T13:31:46","modified_gmt":"2025-11-28T12:31:46","slug":"javascript-testing-jasmine-customization","status":"publish","type":"post","link":"https:\/\/demo.sidekick.be\/itenium\/blog\/javascript\/javascript-testing-jasmine-customization\/","title":{"rendered":"JavaScript Testing: Jasmine customization"},"content":{"rendered":"

Custom equality testers<\/h1>\n

If custom equality testers are provided, they will be checked first before the default equality logic when calling toEqual()<\/code>.<\/p>\n

beforeEach(function() {\n  const myCustomEquality = function(first, second) {\n    if (first === 'everything' && typeof second === 'number') {\n      \/\/ return true or false as final result of .toEqual()\n      return second === 42;\n    }\n    \/\/ return undefined to let the next equality tester give it a shot\n    return undefined;\n  };\n\n  jasmine.addCustomEqualityTester(myCustomEquality);\n});\n\nit('should use myCustomEquality', function() {\n  expect('everything').toEqual(42);\n});\n\nit('should not use myCustomEquality', function() {\n  expect('something').not.toEqual(42);\n});\n<\/code><\/pre>\n
Custom matchers<\/h1>\n
beforeEach(function() {\n  const customMatchers = {\n    toBeDivisibleBy: function(util, customEqualityTesters) {\n      return {\n        compare: function(actual, expected) {\n          var result = {pass: (actual % expected) === 0};\n          if (!result.pass) {\n            \/\/ failure message\n            result.message = `${actual} is not divisible by ${expected} (mod: ${actual % expected})`;\n          } else {\n            \/\/ failure message - when .not.toBeDivisibleBy() fails\n            \/\/ if a negativeCompare function is provided, this message will never be displayed\n            result.message = `${actual} is divisible by ${expected} (mod: ${actual % expected})`;\n          }\n          return result;\n        },\n        \/\/ Optional function when you need more control for the .not case\n        \/\/negativeCompare: function(actual, expected) {}\n      };\n    }\n  };\n\n  jasmine.addMatchers(customMatchers);\n});\n\nit('is divisible by 2', function() {\n  \/\/ The parameter names of the compare function\n  const actual = 14;\n  const expected = 2;\n  expect(actual).toBeDivisibleBy(expected);\n});\n<\/code><\/pre>\n
The customMatcher functions parameters are util<\/code><\/a> and customEqualityTesters<\/code>, the latter is passed to utils functions.<\/p>\n
const util = {\n  equals: function(a, b, customEqualityTesters, diffBuilder),\n  contains: function(haystack, needle, customEqualityTesters),\n};\n<\/code><\/pre>\n
Environment and globals<\/h1>\n
Files included in the jasmine.json<\/code> \u201chelpers\u201d wildcard(s) can provide convenience functions, global variables as well as custom equality testers and matchers.<\/p>\n
Helpers.js:<\/p>\n
beforeEach(function() {\n  \/\/ Custom equality testers and matchers\n  const myExternalCustomEquality = function(first, second) {\n    if (first === 'wuuk' && typeof second === 'number') {\n      return second === 42;\n    }\n  };\n\n  jasmine.addCustomEqualityTester(myExternalCustomEquality);\n  \/\/jasmine.addMatchers(customMatchers);\n\n\n  \/\/ Convenience fuctions, available in it, beforeEach, etc\n  this.yourHelper = function() {\n    return 'as defined';\n  };\n\n\n  \/\/ Mock global variables in required modules\n  jasmine.getGlobal().t = t => t;\n});\n<\/code><\/pre>\n
Some suite:<\/p>\n
describe('Convenience stuff loaded by spec\/helpers\/helpers.js', function() {\n  it('should use myExternalCustomEquality', function() {\n    expect('wuuk').toEqual(42);\n  });\n\n\n  it('can provide helper functions', function() {\n    expect(this.yourHelper()).toBe('as defined');\n  });\n\n\n  it('can set global variables on jasmine.getGlobal()', function() {\n    const globalz = require('.\/global.js');\n    \/\/global.js:\n    \/\/ module.exports = {aGlobalUsingFunction: val => t(val)};\n    \/\/helpers.js:\n    \/\/ jasmine.getGlobal().t = t => t;\n    expect(globalz.aGlobalUsingFunction('ouch')).toBe('ouch');\n  });\n});\n<\/code><\/pre>\n
Some global Jasmine settings:<\/p>\n
it('has default timeout of 5000ms', function() {\n  expect(jasmine.DEFAULT_TIMEOUT_INTERVAL).toBe(5000);\n});\n\nit('can change the pretty printing limits', function() {\n  expect(jasmine.MAX_PRETTY_PRINT_ARRAY_LENGTH).toBe(50);\n  expect(jasmine.MAX_PRETTY_PRINT_DEPTH).toBe(8);\n  expect(jasmine.MAX_PRETTY_PRINT_CHARS).toBe(1000);\n});\n\nit('has its own jasmine.getEnv()', function() {\n  expect(Object.keys(jasmine.getEnv())).toContain('beforeEach');\n});\n<\/code><\/pre>\n
Also in this series<\/h1>\n