Node.js tutorial

Assertion

Node.js has built-in assertion module.

// add assertion module
const assert = require('assert'); 

...
// using 
assert(true); // ok
assert(1); // ok
assert(typeof 123 === 'string'); // fail

Below list of most useful methods.

method description
ok(v [, msg]) Tests if v is truthy. It is equivalent to assert.equal(!!value, true, message). It is alias for call function operator, i.e. assert.ok(v) same as assert(v).
strictEqual(v, expd [, msg]) Tests strict equality between the v and expd parameters.
notStrictEqual(v, expd [, msg]) Tests strict equality between the v and expd parameters.
deepStrictEqual(v, expd [, msg]) Tests for deep equality between the v and expd parameters. "Deep" equality means that the enumerable "own" properties of child objects are recursively evaluated also by the following rules.
notDeepStrictEqual(v, expd [, msg]) Tests for deep equality between the v and expd parameters.
fail(msg) Throws an AssertionError with the provided error message or a default error message. If the message parameter is an instance of an Error then it will be thrown instead of the AssertionError.
ifError(v) Throws v if v is not undefined or null. This is useful when testing the error argument in callbacks.

Chai framework

Chai is available for both node.js and the browser using any test framework you like. There are also a number of other tools that include Chai.

# install chai on Node.js
npm install chai

Recommend adding it to package.json devDependencies using a * as the version tag. 

"devDependencies": {
  "chai": "*",
  "mocha": "*"
},

Chai supports several assertion interfaces. "Assert" style extends api of built-in Node.js assert module.

// add chai framework
var assert = require('chai').assert;

...
// using
assert.typeOf(foo, 'string'); // without optional message
assert.typeOf(foo, 'string', 'foo is a string'); // with optional message
assert.equal(foo, 'bar', 'foo equal `bar`');
assert.lengthOf(foo, 3, 'foo`s value has a length of 3');
assert.lengthOf(beverages.tea, 3, 'beverages has 3 types of tea');

For using in browser you need add chai script file, which define global object chai.

<script src="chai.js" type="text/javascript"></script>
...
<script>
describe('test suite', function() {
    it('some tst', function() {
        chai.assert(true);
    });
});
...
</script>

See more about Chai framework on official site.