A small and simple Javascript test runner

test_runner.js

/**
 * A Javascript test runner in 20 lines of code
 * From http://joakimbeng.eu01.aws.af.cm/a-javascript-test-runner-in-20-lines/
 */
(function () {
  // The test queue:
  var tests = [];

  // Function to add tests:
  this.test = function test (name, cb) {
    tests.push({name: name, test: cb});
  };

  this.run = function run () {
    var i = 0, testToRun;
    (function next (err) {
      // Log status for last test run:
      if (testToRun) console[err ? 'error' : 'log'](err ? '✘' : '✔', testToRun.name);
      // Abort if last test failed or out of tests:
      if (err || !(testToRun = tests[i++])) return done(err);
      // Run test:
      try {
        testToRun.test.call(testToRun.test, next);
      } catch (err) {
        next(err);
      }
    })();
    function done (err) {
      // Show remaining tests as skipped:
      tests.slice(i).map(function (skippedTest) { console.log('-', skippedTest.name); });
      // We're finished:
      console[err ? 'error' : 'log']('\nTests ' + (err ? 'failed!\n' + err.stack : 'succeeded!'));
    }
  };
})();

// Example usage:

test('1+1 equals 2', function (done) {
  assert(1+1 === 2, '1+1 should be 2');
  done();
});
test('1+2 equals 3', function (done) {
  assert(1+2 === 3, '1+2 should be 3');
  done();
});
// Add a failing test:
test('1+2 equals 4', function (done) {
  assert(1+2 === 4, '1+2 should also be 4');
  done();
});

// Run all tests:
run();

// World's smallest assertion library by @snuggsi (https://twitter.com/snuggsi/status/565531862895169536): 
function assert (condition, message) {
  if (!condition) throw new Error(message);
}

Add the following to line 24 and you no longer need to call done manually if you have a synchronous test:

if (!testToRun.test.length) next();

The first test will now look like this:

test('1+1 equals 2', function () {
  assert(1+1 === 2, '1+1 should be 2');
});

See my fork for the complete picture.

I also made it so that you don't need to specially call run. Enjoy!