mocha

What is mocha?

Mocha is a feature-rich JavaScript test framework running on Node.js and in the browser, making asynchronous testing simple and fun. Mocha tests run serially, allowing for flexible and accurate reporting, while mapping uncaught exceptions to the correct test cases.

What are mocha's main functionalities?

Test Organization

Organize tests in suites and sub-suites using describe() and context(), and specify test cases using it().

"use strict";\nconst assert = require('assert');\ndescribe('Array', function() {\n  describe('#indexOf()', function() {\n    it('should return -1 when the value is not present', function() {\n      assert.equal([1, 2, 3].indexOf(4), -1);\n    });\n  });\n});

Asynchronous Testing

Support for testing asynchronous code with ease, using callbacks, promises, or async/await.

"use strict";\nconst assert = require('assert');\ndescribe('User', function() {\n  describe('#save()', function() {\n    it('should save without error', function(done) {\n      const user = new User('Luna');\n      user.save(function(err) {\n        if (err) done(err);\n        else done();\n      });\n    });\n  });\n});

Hooks

Lifecycle hooks such as before(), after(), beforeEach(), and afterEach() for setting up preconditions and clean-up after tests.

"use strict";\ndescribe('Connection', function() {\n  before(function() {\n    // runs once before the first test in this block\n  });\n\n  after(function() {\n    // runs once after the last test in this block\n  });\n\n  beforeEach(function() {\n    // runs before each test in this block\n  });\n\n  afterEach(function() {\n    // runs after each test in this block\n  });\n\n  // test cases\n});

Other packages similar to mocha

jest

Jest is a delightful JavaScript Testing Framework with a focus on simplicity. It works out of the box for any React project and is often compared to Mocha for its comprehensive feature set including a built-in assertion library and mock functions.

jasmine

Jasmine is a behavior-driven development framework for testing JavaScript code. It does not rely on browsers, DOM, or any JavaScript framework. Thus, it's suited for websites, Node.js projects, or anywhere that JavaScript can run. It's compared to Mocha for its clean syntax and testing capabilities.

ava

AVA is a test runner for Node.js with a concise API, detailed error output, and process isolation that lets you develop with confidence. It is often compared to Mocha for its modern, concurrent testing features, but differs in its approach to running tests in parallel by default.

README

mocha

Mocha is a simple, fun, extensible JavaScript test framework rich with features, running on node and the browser. Mocha tests run serially, allowing reporting flexibility, and mapping uncaught exceptions to the correct test cases; This also makes Mocha an ideal choice when mocking and stubbing is involved.

Mocha allows you to use any assertion library you want, if it throws an error, it will work. This means you can utilize libraries such as should, node's regular assert module, or others.

Testing asynchronous code with Mocha could not be simpler, when your tests are sync simple omit the callback, when they are async add a callback and invoke it when your test is complete.

Features

• proper exit status for CI support etc
• ideal for asynchronous APIs
• auto-detects and disables coloring for non-ttys
• maps uncaught exceptions to the correct test case
• async test timeout support
• growl notification support
• reports test durations
• highlights slow tests
• global variable leak detection
• configurable test-case timeout
• optionally run tests that match a regexp
• auto-exit to prevent "hanging" due to an active event loop
• easily meta-generate suites & test-cases
• mocha.opts file support
• mocha-debug(1) for node debugger support
• detects multiple calls to done()
• TextMate bundle
• use any assertion library you want (should, assert, etc)
• extensible reporting
  • dot: a dot matrix
  • doc: a documentation generator (html) based on your tests
  • landing: a unicode landing strip ✈
  • tap: test-anything-protocol (TAP) producer
  • progress: a progress bar
  • spec: hierarchical specification
  • list: similar to spec as a flat-list
  • json-stream: streaming JSON delimited by a LF
  • json: a single JSON chunk on exit
• extensible test DSLs
  • BDD
  • TDD
  • exports

Usage

Usage: mocha [options] [files]

Options:

  -h, --help             output usage information
  -V, --version          output the version number
  -r, --require <name>   require the given module
  -R, --reporter <name>  specify the reporter to use
  -u, --ui <name>        specify user-interface (bdd|tdd|exports)
  -g, --grep <pattern>   only run tests matching <pattern>
  -t, --timeout <ms>     set test-case timeout in milliseconds [2000]
  -s, --slow <ms>        "slow" test threshold in milliseconds [75]
  -G, --growl            enable growl support

Reporters:

  dot - dot matrix
  doc - html documentation
  json - single json object
  progress - progress bar
  list - spec-style listing
  tap - test-anything-protocol
  landing - unicode landing strip
  json-stream - newline delimited json events

Interfaces:

  bdd - describe() / it()
  tdd - suite() / test()
  exports - module.exports

Interfaces

Mocha "interfaces" providing BDD, TDD, and expresso export-style flavoured APIs on top of the internals.

BDD

describe('Array', function(){
  before(function(){
    // ...
  });

  describe('#indexOf()', function(){
    it('should return -1 when not present', function(){
      [1,2,3].indexOf(4).should.equal(-1);
    });

    it('should return the index when present', function(){
      [1,2,3].indexOf(3).should.equal(2);
      [1,2,3].indexOf(2).should.equal(1);
      [1,2,3].indexOf(1).should.equal(0);
    });
  });
});

TDD

suite('Array', function(){
  setup(function(){
    // ...
  });

  suite('#indexOf()', function(){
    test('should return -1 when not present', function(){
      assert.equal(-1, [1,2,3].indexOf(4));
    });

    test('should return the index when present', function(){
      assert.equal(2, [1,2,3].indexOf(3));
      assert.equal(1, [1,2,3].indexOf(2));
      assert.equal(0, [1,2,3].indexOf(1));
    });
  });
});

Exports

module.exports = {
  'Array': {
    '#indexOf()': {
      'should return -1 when not present': function(){
        [1,2,3].indexOf(4).should.equal(-1);
      },
      
      'should return the index when present': function(){
        [1,2,3].indexOf(3).should.equal(2);
        [1,2,3].indexOf(2).should.equal(1);
        [1,2,3].indexOf(1).should.equal(0);
      }
    }
  }
};

Reporters

Mocha reporters adjust to the terminal window, and always disable ansi-escape colouring when the stdio streams are not associated with a tty.

Dot Matrix

The Dot Matrix reporter is simply a series of dots that represent test cases, failures highlight in red.

TAP

The TAP reporter emits lines for a Test-Anything-Protocol consumer.

Landing Strip

The Landing Strip reporter is a gimmicky test reporter simulating a plane landing :) unicode ftw

List

The "List" reporter outputs a simple specifications list as test cases pass or fail, outputting the failure details at the bottom of the output.

JSON

The JSON reporter outputs a single large JSON object when the tests have completed (failures or not).

JSON Stream

The JSON Stream reporter outputs newline-delimited JSON "events" as they occur, beginning with a "start" event, followed by test passes or failures, and then the final "end" event.

["start",{"total":12}]
["pass",{"title":"should return -1 when not present","fullTitle":"Array #indexOf() should return -1 when not present","duration":0}]
["pass",{"title":"should return the index when present","fullTitle":"Array #indexOf() should return the index when present","duration":0}]
["fail",{"title":"should return -1 when not present","fullTitle":"Array #indexOf() should return -1 when not present"}]
["end",{"start":"2011-08-29T03:21:02.050Z","suites":13,"passes":11,"tests":12,"failures":1,"end":"2011-08-29T03:21:02.052Z","duration":2}]

Doc

The "doc" reporter outputs a hierarchical HTML body representation of your tests, wrap it with a header, footer, some styling and you have some fantastic documentation!

For example suppose you have the following JavaScript:

describe('Array', function(){
  describe('#indexOf()', function(){
    it('should return -1 when the value is not present', function(){
      [1,2,3].indexOf(5).should.equal(-1);
      [1,2,3].indexOf(0).should.equal(-1);
    })
  })
})

The command mocha --reporter doc array would yield:

<section class="suite">
  <h1>Array</h1>
  <dl>
    <section class="suite">
      <h1>#indexOf()</h1>
      <dl>
      <dt>should return -1 when the value is not present</dt>
      <dd><pre><code>[1,2,3].indexOf(5).should.equal(-1);
[1,2,3].indexOf(0).should.equal(-1);</code></pre></dd>
      </dl>
    </section>
  </dl>
</section>

Async tests

Testing async code with mocha is simple, invoke the done() callback when complete, if called multiple times (due to a race-condition etc) will cause mocha to fail, this is invaluable for testing async code.

describe('something async', function(){
  it('should finish after 300ms', function(done){
    setTimeout(done, 300);
  })
})

The done() callback also accepts an error, so it's easy to write tests that adhere to node's callback convention of (err, result):

describe('User.save()', function(){
  it('should save without failing', function(done){
    var user = new User('tj');
    user.save(done);
  })
})

Best practices

test/*

By default mocha(1) will use the pattern ./test/*.js, so it's usually a good place to put your tests.

mocha.opts

Mocha will attempt to load ./test/mocha.opts, these are concatenated with process.argv, though command-line args will take precedence. For example suppose you have the following mocha.opts file:

--require should
--reporter dot
--ui bdd

This will default the reporter to dot, require the should library, and use bdd as the interface. With this you may then invoke mocha(1) with additional arguments, here enabling growl support and changing the reporter to spec:

$ mocha --reporter list --growl

Suite merging

Suites with common names are "merged" in order to produce unified reporting, especially when meta-generating tests.

describe('merge', function(){
  describe('stuff', function(){
    describe('one', function(){
      it('should do something', function(){
        
      })
    })
  })
})

describe('merge', function(){
  describe('stuff', function(){
    describe('two', function(){
      it('should do something', function(){
        
      })
    })
  })
})

describe('merge stuff', function(){
  describe('three', function(){
    it('should do something', function(){
      
    })
  })
})

will produce the following:

Makefiles

Be kind and don't make developers hunt around in your docs to figure out how to run the tests, add a make test target to your Makefile:

test:
  ./node_modules/.bin/mocha \
    --reporter list

.PHONY: test

TextMate Bundle

The Mocha TextMate bundle includes snippets to make writing tests quicker and more enjoyable. To install the bundle run:

 $ make tm

Running tests

Run mocha tests:

 $ make test

Run all tests, including interfaces:

 $ make test-all

Alter the reporter:

 $ make test REPORTER=list

License

(The MIT License)

Copyright (c) 2011 TJ Holowaychuk <[e-mail]>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.