works with jasmine v2 (for work with jasmine v1.3 see jasmine-custom-message)

This script makes it possible to use your own failure message on any jasmine assertion.

describe('the story', function() {
  it('should finish ok', function() {
    since('all cats are grey in the dark').
    expect('tiger').toEqual('kitty'); // => 'all cats are grey in the dark'
  });
});

All the magic happens in since function. That returns an object with a property expect. That contains no more than a wrapped jasmine expect function. That returns jasmine expectation object with a wrapped addExpectationResult function. That can replace an ordinary jasmine failure message with a newly generated one. That is generating based on a custom message you have supplied to since function as the first argument. That can be a primitive (except null and undefined), a function, or any other object. That is it.

describe('test', function() {
  it('should be ok', function() {
    since(function() {
      return {'tiger': 'kitty'};
    }).
    expect(3).toEqual(4); // => '{"tiger":"kitty"}'
  });
});

You can use jasmine as you did before, since jasmine2-custom-message does not replace global jasmine expect function.

describe('test', function() {
  it('should be ok', function() {
    expect(3).toEqual(4); // => ordinary jasmine message
  });
});

You can use expected and actual values of the assertion in your custom message by:

• Passing a function, and using this.actual and this.expected
• Passing a string, and using #{actual} and #{expected}

You can include the full original message from Jasmine by:

• Passing a function, and using this.message
• Passing a string, and using #{message}

describe('test', function() {
  it('should be ok', function() {
    since(function() {
      return this.actual + ' =/= ' + this.expected;
    }).
    expect(3).toEqual(4); // => '3 =/= 4'
  });
});

describe('multiple tests that need some context added to the message', function() {
    it('should be ok for all options', function() {
      // passes the 1st loop iteration, fails the 2nd
      [1, 2, 3, 4, 5].forEach(testOptionIndex => {
        since(function() {
          return 'for test option ' + testOptionIndex + ': ' + this.message;
        }).
        expect(testOptionIndex).toEqual(1); // => for test option 2: Expected 2 to equal 1.  
      });
    });
});

describe('test', function() {
  it('should be ok', function() {
    since('#{actual} =/= #{expected}').
    expect(3).toEqual(4); // => '3 =/= 4'
  });
});

describe('multiple tests that need some context added to the message', function() {
    it('should be ok for all options', function() {
      // passes the 1st loop iteration, fails the 2nd
      [1, 2, 3, 4, 5].forEach(testOptionIndex => {
        since('for test option ' + testOptionIndex + ': #{message}').
        expect(testOptionIndex).toEqual(1); // => for test option 2: Expected 2 to equal 1.  
      });
    });
});

• install the bower package from github

bower install jasmine2-custom-message --save-dev

• include jasmine2-custom-message.js into your HTML file next to jasmine script

<script src="PATH-TO/jasmine.js"></script>
<script src="PATH-TO/jasmine2-custom-message.js"></script>

• install the bower package from github

$ bower install jasmine2-custom-message --save-dev

or

$ npm install jasmine2-custom-message --save-dev

• require it in your spec file before your tests

require('jasmine2-custom-message');

• or be explicit in any functional scope

var since = require('jasmine2-custom-message');

v0.9.0 - 2018.03.01

• improved "format string" functionality: #{message} added for the original jasmine2 error message (kudos to Keith Zimmerman)
• corrected output for toHaveBeenCalled matcher (kudos to Holger Jeromin)
• updated protractor environment (kudos to Keith Zimmerman)
• added typescript definitions (kudos to Holger Jeromin and Andrew N Marshall)
• updated specs

v0.8.0 - 2015.08.05

• implemented "format string" functionality: #{actual} and #{expected}
• configured protractor environment
• corrected displaying of colors in tests running through protractor
• updated specs

v0.7.0 - 2014.10.23

• fixed issue with custom failure messages on inverse assertions
• updated specs

v0.6.0 - 2014.01.18 - BROKEN COMPATIBILITY!

• all the magic moved into newly introduced since function
• restored automatic initiation of the script upon inclusion (browser) or require (Node.js)
• cleaned specs

v0.5.0 - 2014.01.15

• added support for nested message functions
• dropped automatic wrapping of jasmine it and expect functions in browsers
• added specs for Node.js
• added specs for browsers
• registered bower package
• made disambiguation and readability improvements

v0.2.0 - 2014.01.10

• BROKEN COMPATIBILITY: custom messages is supplied as the third argument for jasmine it function

v0.1.0 - 2014.01.08

• the first functional version

v1.0.0 - some new features and updates (based on requests from Issues)