consert

This little script is designed to serve as an introduction to testing.

It is specifically targeted towards the beginner/novice however if you are a seasoned developer, feel free to follow along.

Introduction

The task is simple.

In order to understand how testing works, you will attempt to build a miniature testing framework using vanilla javascript in your preferred environment.

We recommend using the browser console so you can follow along as you code for a more hands on experience.

Let's get started!

Analysis & Design

The framework will use console.assert as the core to run assertion tests.

Take a moment to think about how the framework will be used because that is the framework's API.

For simplicity, the framework will use the callback pattern illustrated below.

test(description, callback);

This is a common pattern in a number of frameworks such as ava where assertions happen within the callback function. The description works like an id for tracking passing and failing tests.

For simplicity, the callback function will receive only one parameter - the assertion object which holds the API.

The API will closely resemble ava's hence a general idea of how the framework will work is illustrated below.

test("it should do something", c => {
  c.is(expected, actual); // checks equality
  c.notEqual(expected, actual); // checks inequality
  c.true(condition); // checks condition
})

Implementation

Nothing too complex. Only about 22 LLOC

var assert, // the object that will hold the api
message; // provides more context for failing tests

assert = {} // initialize empty object
// TODO: assert.is = is;
// TODO: assert.notEqual = notEqual;
// TODO: assert.true = truthy;

/**
  * Test
  * @param {any} description - Test description
  * @param {any} callback - Test function
*/
function test(description, callback) {
  callback(assert);
}

The function above runs the callback function which in turn runs the assertions within it hence executing the test.

Go ahead and implement the is feature that will be used to run simple equality checks as shown below (comments not required).

/**
  * Checks equality
  * @param {any} expected - Expected value
  * @param {any} actual - Actual value
*/
function is(expected, actual) {
  message = `Expected ${expeced} but received ${actual}`;
  console.assert(expected === actual, { message });
}

assert.is = is;

Simply put the function above compares the actual value to the expected value using strict equality. If the check FAILS, it will output the message provided.

Go ahead and test it.

test("1 should equal 1", assert => {
  assert.is(1, 1); // pass
});

test("2 should equal 2", check => {
  check.is(2, "2"); // fail
});

test("true should be true", verify => {
  verify.is(true, true); // pass
});

test("false should be false", confirm => {
  confirm.is(false, true); // fail
});

As you can see the argument name doesn't matter. Use whatever works for you but aim for legibility and simplicity.