How To Write A Java Script Code – We all know that we should write unit tests. But it’s hard to know where to start and how much time to spend on testing compared to actual implementation. So, where do we start? And is it just about code testing or does unit testing have other benefits?
How To Write A Java Script Code
Before we get into the details of unit testing, I want to quickly review the different types of tests. There is often confusion around them and I am not surprised. Sometimes the line between them is very thin.
Unit tests only test part of your implementation. one. No dependency or integration, no specific framework. These are like methods that return a link to a specific language:
At some point, your code interacts with a database, file system, or other third party. It can also be another module in your app.
That part of the implementation should be tested with integration testing. They usually have a more complex setup that includes creating a test environment, initializing dependencies, etc.
Unit tests and integration tests ensure that your application works. Functional tests look at the application from the user’s point of view and check that the system works as expected.
In the figure above, you can see that unit tests make up the bulk of your application’s test suite. Usually they are small, there are a lot of them and they run automatically.
Whenever I ask developers if they write tests for their apps, they always tell me, “I don’t have time for them” or “I don’t need them, I know it works.”
So I smile politely and tell them what I want to tell you. Unit testing is not just testing. They also help you in other ways, so you can:
Make sure your code works. The last time you changed code, your build failed and half of your app crashed? Mine was last week
But it’s still okay. The real problem is that when the build succeeds, the change is committed and your program starts to become unstable.
When this happens, you lose faith in your code and pray that the program will finally work. Unit testing helps you discover problems much earlier and gain confidence.
Make better architectural decisions. Code changes, but some decisions about platforms, modules, frameworks, etc. need to be made early in a project.
When you first start thinking about unit testing, it helps you better structure your code and achieve a proper separation of concerns. Don’t be tempted to assign multiple responsibilities to single code blocks as this is a nightmare for unit testing.
Identify functionality before coding. You write the method signature and start executing it immediately. Oh, but what if a parameter is null? What if the value is outside the expected range or has too many characters? Do you throw an exception or return null?
Unit tests help you explore all these areas. Look at the questions again and you will see exactly what your unit test is about.
I’m sure there are many more benefits to writing unit tests. These are just reminders of my experience. That I learned the hard way
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File We can write the tests in one file, but a good practice is to separate the unit tests in a dedicated file.
First we need to enter the function we want to test. Each test is defined as a call
The first function parameter is the test name for your reference. The other is a flash function where we call the function we want to test and specify what result we expect. I am
Once you save the file, Jest will tell you that the test failed. This will help you identify potential problems before you even make your changes
In real life, the language code of the getAboutUsLink method will not be in a static file. Their values are usually used throughout the project, so they are defined in their own module and imported into all functions that use them.
You can enter these constants in tests in the same way. If you’re dealing with objects instead of simple constants, the situation gets more complicated. Pay attention to this method:
. A mock is a replacement for the original object. This allows us to separate dependencies and real data from the execution of the method being tested, just as mocks instead of real people assist in car crash testing.
If we don’t use mock, we test both this function and the store. This will be an integration test and we will probably need to mock the database being used.
To mock objects, you can provide a mock function or a manual mock. I will focus on the latter because I have a simple and common use case. But feel free to check out the other mocking features provided by Jest
. But with a real performance, the fake can be much longer. Any functionality you don’t really care about can easily be mocked in the scope of a unit test
As soon as I save the file, the search tells me that I have passed 2 tests. If you run the test manually, do it now and make sure you see the same results.
Code coverage tells you how much of your code is covered by unit tests. Take my first unit test as an example
It checks the English link, but the Spanish version remains unchecked. Code coverage is 50%. Other tests are unit tests
It is fully functional and has 100% code coverage. In total, the total code coverage is 67%. We had 3 test cases, but our tests only covered 2.
. This will show you in the implementation which lines of code are not covered by the test.
When you run a coverage check, Jest also generates an HTML report. Find it in your project folder below
The best place to start is the Jest documentation start page, so you can try these methods for yourself.
Do you have experience with code testing? I’d love to hear it, let me know on Twitter or join one of my Twitch streams.
Jamstack developer, YouTube video maker and streamer, @content development promoter, 3D printing enthusiast, AoE2 bad player, German Shepherd lover
👩🏻💻 Finally, understanding how real project files are structured and referenced will help you get started.
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