Node: Up and Running

Testing Through assert

assert is a core library that provides the basis for testing code. Node’s assertions works pretty much like the same feature in other languages and environments: they allow you to make claims about objects and function calls and send out messages when the assertions are violated. These methods are really easy to get started with and provide a great way to unit test your code’s features. Node’s own tests are written with assert.

Most assert methods come in pairs: one method providing the positive test and the other providing the negative one. For instance, Example 5-37 shows equal() and notEqual(). The methods take two arguments: the first is the expected value, and the second is the actual value.

Example 5-37. Basic assertions

> var assert = require('assert');
> assert.equal(1, true, 'Truthy');
> assert.notEqual(1, true, 'Truthy');
AssertionError: Truthy
    at [object Context]:1:8
    at Interface.<anonymous> (repl.js:171:22)
    at Interface.emit (events.js:64:17)
    at Interface._onLine (readline.js:153:10)
    at Interface._line (readline.js:408:8)
    at Interface._ttyWrite (readline.js:585:14)
    at ReadStream.<anonymous> (readline.js:73:12)
    at ReadStream.emit (events.js:81:20)
    at ReadStream._emitKey (tty_posix.js:307:10)
    at ReadStream.onData (tty_posix.js:70:12)
>

The most obvious thing here is that when an assert method doesn’t pass, it throws an exception. This is a fundamental principle in the test suites. When a test suite runs, it should just run, without throwing an exception. ...