Writing robust Vue.js unit tests using Avoriaz

Introduction

Writing unit tests is a critical step in building robust, high quality software. When developing Vue.js applications, it is often helpful to write unit tests that make assertions on components and how they are rendered.

In this article we’ll look at writing unit tests for Vue.js applications using Avoriaz, a testing utility library for Vue.js.

For this piece, Vue refers to Vue.js 2.x versions.

Note that a basic understanding of Vue, with the webpack template is required to follow this guide.

Setting Up Our Environment

To get started with our project, we will use the Vue-cli . This would help us to skip the process of configuring webpack and all other complicated processes.

If you do not have the Vue-cli installed, we can do so by running the following command:

npm install -g vue-cli

Once we have the vie-cliinstalled, let’s proceed to creating the application. To do that, we run:

vue init webpack unittest

At this stage, you’ll be prompted with a few questions. You can accept the default option for most of them, the only requirement is that you answer YES to including vue-router and YES to setting up unit tests with Karma and Mocha.

Understanding The Default Test

Next, Let us take a look at our test\unit\specs\Hello.spec.js . We will notice this block of code:

In the code block above, we will notice:

• The import of Vue library
• The import of our Hello component
• The description of the test, named Hello.vue
• One unit test which says “should render correct content”. Under this test, we mount our component, then declare our expect function, which checks to see that the output is equal to what we are expecting.

Notice that in the test above, we expected that the text content of the h1 tag under the hello class would be equal to welcome to Your Vue.js App

This explains how simple it is for a Vue test to be written. As simple as this method is, there is a simpler method to write tests in Vue.

Writing Vue Tests using Avorias

Remember i mentioned that there is a simpler method for writing unit test in Vue. Here we are. That simple method is using a package called avorias .

First, we need to install the package. To do that, let us run the following commands.

// change directory to our folder
cd unittest
// install the avorias package
npm install avoriaz

Now let us re-write the default hello test using avoriaz . To do that, let us delete the test\unit\specs\Hello.spec.js file, then create a new file called test\unit\specs\Hello-avorias.spec.js .

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After creating this file, let us replace its content with:

Looking at the above code block, we notice the following differences from the default test spec

• We import mount as opposed to Vue in the default test. This is because avorias comes with a mount helper function, as opposed to extending Vue, then mounting it.
• We used thetext() function rather than using the textContent property. This is because avorias gives us a helper function called text()

Creating Our Testable Component

Let us create a new file called Happy.vue in our src\components folder and paste in the following content:

Let’s have a quick explanation of what we have in the code-block above.

• Our template section comprises one div (root element) which comprise a looped h1 tag.
• We declared our data comprising just one variable called them which is looped in the template section.
• In our mounted call, we called the function called get_them
• The get_them function uses axios to send a GET request to https://restcountries.eu/rest/v2/all. However, we do not use the response. We only use it to fire and async event.
• Finally, we have two computed properties. One which adds a new item to the them array and returns it. The second computed property returns a string happy

Next, we will look at how to test our new component. This means we will test our get_them function, and our computed properties.

Updating Our Routes

Next, we need to update our routes, so we can have a view of the component we have built so far. To do this, let’s open our src\router\index.js and replace it with:

In the code block above, we have imported our happy component and added it to our routes.

If we run npm run dev in our terminal and browse to http://localhost:8080/#/happy we should see the following image:

Testing Our Components Methods

Now, let us test. If we inspect our method calledget_them , we notice that we had an async call using axios . Because of this, if we attempt to write tests for our component, we will run into various issues such as:

• Promise is undefined
• Timeout of 2000ms exceeded.

To take care of these issues during testing, we will install two libraries which are:

• Promise: To solve “cannot find variable Promise / Promise is undefined”
• Moxios: This library would stub requests and return fake data into it. So as to fake early completion of our async call.

To install these libraries, we run:

npm install promise moxios

Now we have these libraries installed, let us create a new file called Happy-avorias.spec.js in our test\unit\specs\ folder. Let us add the following code into the file:

Let’s understand what we have done on the code block above:

• We imported our mount function as we have explained before
• Next, we imported Moxios for stubbing request.
• We then set a global variable called Promise to the instance of our Promise library. This is so we don’t face issues like promise is not defined from Axios.
• We then described our test
• We called two hooks called beforeEach and afterEach to handle the installation and un-installation of Moxios . This means Moxios will be installed before all tests defined in this file, and will be uninstalled after each test.
• We defined two test criteria
• In the first test criteria, we used Moxios to catch the request going to https://restcountries.eu/rest/v2/all and then return a test data.
• we use moxios.wait to ensure that the promise is resolved before declaring our expect keyword
• Notice we use vm.data() to access a data property of our component? This is a helper function provided by avorias
• We check that our data has happy one as part of the content in its array, which was assigned to it after the request.
• In the second test criteria, we also used Moxios to stub requests. However, here we found out that the length of our array is equal to 4. which is the length of array we are expecting.

Testing Our Computed Data

Just above, we have seen how to test data, and methods. Here we move into testing computed properties. Testing computed properties with avorias can be a little tricky as this isnt bound to computed properties. Refer to the link below about the issue.

However, fear not. We will cover how to solve this issue while running our own tests on computed properties.

Let us go back to our Happy-avorias.spec.js and replace it with the following content:

In the code block above, we will notice the addition of two new test criteria.

• The first criteria says it must return computed data. It checks for the response of our computed_first() property which does nothing with the this keyword.
• Note the helper function computed() by avorias for checking computed properties
• The second criteria says it should have a length of 5. However, the computed property referenced here all_of_them uses the this keyword which avorias does not bind to computed property
• Notice that instead of expecting app.computed().all_of_them() , we expected app.vm.all_of_them to contain computed_one

Explained above is the only difference we need to take into consideration while running computed data. Also, please be informed that the same issue applies to props data.

We can run all our tests by running:

npm run unit

we should get the following results:

Conclusion

Writing unit tests in Vue is as essential as writing your application itself. Most users would not return to an application that has bugs. The easiest way to minimize this bugs to the barest minimum is by writing accurate unit tests.

In this little piece, we have gone through how to write unit tests for Vue using the avorias package.

The codebase to this little guide can be found here: samuelayo/vue-unit-test

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