Unit Testing Basics

Unit Testing Basics

Unit tests are generally used to test a small piece of code and ensure that it is doing what was intended. Unlike acceptance tests, they are narrow in scope and do not require the Ember application to be running.

As it is the basic object type in Ember, being able to test a simple Ember.Object sets the foundation for testing more specific parts of your Ember application such as controllers, components, etc. Testing an Ember.Object is as simple as creating an instance of the object, setting its state, and running assertions against the object. By way of example, let's look at a few common cases.

Testing Computed Properties

Let's start by creating an object that has a computedFoo computed property based on a foo property.

import Ember from 'ember';

export default Ember.Object.extend({
  foo: 'bar',

  computedFoo: Ember.computed('foo', function() {
    const foo = this.get('foo');
    return `computed ${foo}`;
  })
});

Within the test for this object we'll create an instance, update the foo property (which should trigger the computed property), and assert that the logic in our computed property is working correctly.

import { moduleFor, test } from 'ember-qunit';

moduleFor('model:some-thing', 'Unit | some thing', {
  unit: true
});

test('should correctly concat foo', function(assert) {
  const someThing = this.subject();
  someThing.set('foo', 'baz');
  assert.equal(someThing.get('computedFoo'), 'computed baz');
});

See that we have used moduleFor, one of the several unit-test helpers provided by Ember-Qunit. Test helpers provide us with some conveniences, such as the subject function that handles lookup and instantiation for our object under test. Note that in a unit test you can customize the initialization of your object under test by passing to the subject function an object containing the instance variables you would like to initialize. For example, to initialize the property 'foo' in our object under test, we would call this.subject({ foo: 'bar' });

Testing Object Methods

Next let's look at testing logic found within an object's method. In this case the testMethod method alters some internal state of the object (by updating the foo property).

import Ember from 'ember';

export default Ember.Object.extend({
  foo: 'bar',
  testMethod() {
    this.set('foo', 'baz');
  }
});

To test it, we create an instance of our class SomeThing as defined above, call the testMethod method and assert that the internal state is correct as a result of the method call.

test('should update foo on testMethod', function(assert) {
  const someThing = this.subject();
  someThing.testMethod();
  assert.equal(someThing.get('foo'), 'baz');
});

In the event the object's method returns a value you can simply assert that the return value is calculated correctly. Suppose our object has a calc method that returns a value based on some internal state.

import Ember from 'ember';

export default Ember.Object.extend({
  count: 0,
  calc() {
    this.incrementProperty('count');
    let count = this.get('count');
    return `count: ${count}`;
  }
});

The test would call the calc method and assert it gets back the correct value.

test('should return incremented count on calc', function(assert) {
  const someThing = this.subject();
  assert.equal(someThing.calc(), 'count: 1');
  assert.equal(someThing.calc(), 'count: 2');
});

Testing Observers

Suppose we have an object that has a property and a method observing that property.

import Ember from 'ember';

export default Ember.Object.extend({
  foo: 'bar',
  other: 'no',
  doSomething: Ember.observer('foo', function() {
    this.set('other', 'yes');
  })
});

In order to test the doSomething method we create an instance of SomeThing, update the observed property (foo), and assert that the expected effects are present.

test('should set other prop to yes when foo changes', function(assert) {
  const someThing = this.subject();
  someThing.set('foo', 'baz');
  assert.equal(someThing.get('other'), 'yes');
});