Vue Unit Testing #2 - Button component test

Summary

In this tutorial, the process of testing a Vue component, the `BaseButton`, is thoroughly explained using the Vtest library. The video covers creating a test file, rendering the component, simulating a browser environment with the `heydo` library, and checking the rendered output. The test validates that the default slot content and correct CSS classes are applied based on the button's type. The tutorial guides users through writing and executing their first test, helping them understand component testing, assertions, and handling Vue's component structure effectively.

Takeaways

• 😀 The first test file for the Vue component, BaseButton, is created inside a 'components' folder under the 'test' directory.
• 😀 The BaseButton component is used to render various buttons, including one for activity deletion, and it accepts a prop called 'type' to determine button styling.
• 😀 The test scenario checks if a primary button is rendered by default when no 'type' prop is specified.
• 😀 Vue's 'Mount' function from the Vue Test Utils library is used to render components in the test environment.
• 😀 The error 'document is not defined' occurs when testing in a Node.js environment because document is browser-specific, requiring an emulation solution.
• 😀 To emulate a browser environment in Node.js, the 'happy-dom' library is used, which is pre-installed in the project.
• 😀 The 'HTML' method on the wrapper object prints the rendered markup of the BaseButton component, showing the button element.
• 😀 A default slot is passed to the BaseButton component to supply content (like button label) when rendering.
• 😀 'expect' function from the 'vest' library is used to assert that the rendered markup contains the content passed into the default slot.
• 😀 The test also checks if the correct CSS classes for a primary button type are applied by comparing the assigned classes to expected values using the 'classes' method.
• 😀 After running the test and adjusting the BaseButton component, the test validates the presence of the correct CSS classes, throwing an error if discrepancies are found.

Q & A

What is the purpose of creating a test file for the base button component?

The test file for the base button component is created to ensure the functionality of the button is working correctly in different scenarios, like rendering the component with default settings or applying the correct classes for different button types.

Why is the file suffix '.dopc' used in the test file?

The suffix '.dopc' is used to indicate that the file contains test code. This helps the testing framework recognize and execute the file as part of the test suite.

What is the role of the 'type' prop in the base button component?

The 'type' prop is used to define the type of button (e.g., primary, danger) and is responsible for determining the CSS classes that are applied to the button to control its style.

What problem does the error 'document object is not defined' indicate, and how is it resolved?

The error occurs because the tests are being run in a Node.js environment where the 'document' object (which is part of the browser environment) is not available. It is resolved by using the 'happy do' library to emulate a browser environment for the tests.

How is the default slot content passed to the base button component in the test?

The default slot content is passed by specifying the 'slots' option in the second parameter of the 'mount' function. The content for the default slot is assigned using the 'default' key.

What is the significance of the 'expect' function in writing assertions for the test?

The 'expect' function is used to define the expected behavior of the component being tested. In this case, it checks if the rendered HTML contains the correct label passed as the default slot.

Why does the test check for the assigned CSS classes in the button?

The test checks the assigned CSS classes to ensure that the correct button type (e.g., primary or danger) is being applied, and the button has the expected styling based on the 'type' prop.

What is the purpose of the 'classes' method in the test?

The 'classes' method returns an array of all the CSS classes assigned to the button element. It is used in the test to verify that the correct classes corresponding to the button type are applied.

How does the test validate that the correct button type is rendered by default?

The test validates that the correct button type is rendered by default by comparing the actual assigned classes with the expected classes for the default button type (primary) using the 'expect' function and assertions.

What would happen if the default value of the 'type' prop was changed, and how does the test reflect this?

If the default value of the 'type' prop was changed (e.g., from primary to danger), the test would fail because it expects the primary button classes. This change would trigger an error in the test, indicating a mismatch in the expected and actual button type classes.