What is testing library ?

If Typescript it’s a superset of Javascript, that takes what javascript does and increases it’s functionality, then Testing Library is exactly the same thing to Jest or other testing frameworks.

Testing Library will run over the most known testing frameworks to the date, increasing their functionality.

Mindset

Using testing library is more similar to end to end testing than unit testing, as it shares the same points of view:

• User behavior centered.
• Ignores implementation details.
• Acts and queries over DOM nodes.

We need to think what the user will expect to see on the screen on each step of the way, so unit testing a component should be checking it’s behavior in relation with the context.

For example, testing a form asking for a username and a password could result in these tests:

• Check that two inputs are on the screen, one for username and the other for password.
• Check that if the user clicks on each input but doesn’t complete it, an error message will appear. We could also check if the inputs have the class to set them in red to notify the user.
• Check that if the user enters wrong information in a field, the input will be validated, an error message appears and that the input has the correct styles.
• Check that if the user enters valid data and clicks on submit, a call to the back with the correct information has been made.

As you can see, we don’t test each method inside the component, but the interaction that the user will have with it. If we reach the desired result, that means that the methods inside are working as expected.

Testing library ——> Creates an HTML and adds the element to be tested inside ( creates a controlled environment )

To do the testing correctly we need:

• Atomicity.