mocha

What are mocha's main functionalities?

"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});

"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});

"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});

8.2.0 / 2020-10-16

The major feature added in v8.2.0 is addition of support for global fixtures.

While Mocha has always had the ability to run setup and teardown via a hook (e.g., a before() at the top level of a test file) when running tests in serial, Mocha v8.0.0 added support for parallel runs. Parallel runs are incompatible with this strategy; e.g., a top-level before() would only run for the file in which it was defined.

With global fixtures, Mocha can now perform user-defined setup and teardown regardless of mode, and these fixtures are guaranteed to run once and only once. This holds for parallel mode, serial mode, and even "watch" mode (the teardown will run once you hit Ctrl-C, just before Mocha finally exits). Tasks such as starting and stopping servers are well-suited to global fixtures, but not sharing resources--global fixtures do not share context with your test files (but they do share context with each other).

Here's a short example of usage:

// fixtures.js

// can be async or not
exports.mochaGlobalSetup = async function () {
  this.server = await startSomeServer({port: process.env.TEST_PORT});
  console.log(`server running on port ${this.server.port}`);
};

exports.mochaGlobalTeardown = async function () {
  // the context (`this`) is shared, but not with the test files
  await this.server.stop();
  console.log(`server on port ${this.server.port} stopped`);
};

// this file can contain root hook plugins as well!
// exports.mochaHooks = { ... }

Fixtures are loaded with --require, e.g., mocha --require fixtures.js.

For detailed information, please see the documentation and this handy-dandy flowchart to help understand the differences between hooks, root hook plugins, and global fixtures (and when you should use each).

:tada: Enhancements

• #4308: Support run-once global setup & teardown fixtures (@boneskull)
• #4442: Multi-part extensions (e.g., test.js) now usable with --extension option (@jordanstephens)
• #4472: Leading dots (e.g., .js, .test.js) now usable with --extension option (@boneskull)
• #4434: Output of json reporter now contains speed ("fast"/"medium"/"slow") property (@wwhurin)
• #4464: Errors thrown by serializer in parallel mode now have error codes (@evaline-ju)

For implementors of custom reporters:

• #4409: Parallel mode and custom reporter improvements (@boneskull):
  • Support custom worker-process-only reporters (Runner.prototype.workerReporter()); reporters should subclass ParallelBufferedReporter in mocha/lib/nodejs/reporters/parallel-buffered
  • Allow opt-in of object reference matching for "sufficiently advanced" custom reporters (Runner.prototype.linkPartialObjects()); use if strict object equality is needed when consuming Runner event data
  • Enable detection of parallel mode (Runner.prototype.isParallelMode())

:bug: Fixes

• #4476: Workaround for profoundly bizarre issue affecting npm v6.x causing some of Mocha's deps to be installed when mocha is present in a package's devDependencies and npm install --production is run the package's working copy (@boneskull)
• #4465: Worker processes guaranteed (as opposed to "very likely") to exit before Mocha does; fixes a problem when using nyc with Mocha in parallel mode (@boneskull)
• #4419: Restore lookupFiles() in mocha/lib/utils, which was broken/missing in Mocha v8.1.0; it now prints a deprecation warning (use const {lookupFiles} = require('mocha/lib/cli') instead) (@boneskull)

Thanks to @AviVahl, @donghoon-song, @ValeriaVG, @znarf, @sujin-park, and @majecty for other helpful contributions!