Custom extensions in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom extension in JUnit?

A custom extension in JUnit is a user-defined class that adds extra behavior to tests, such as setup, teardown, or conditional test execution, by implementing JUnit's Extension API.

beginner

Which JUnit interface do you implement to create a custom extension that runs code before and after each test?

You implement the BeforeEachCallback and AfterEachCallback interfaces to run code before and after each test method.

beginner

How do you register a custom extension in a JUnit 5 test class?

You register a custom extension by annotating the test class with <code>@ExtendWith(YourExtension.class)</code>.

intermediate

What is the purpose of the ExtensionContext parameter in JUnit custom extensions?

The ExtensionContext provides information about the current test, such as test method, test class, and a store for sharing data between callbacks.

intermediate

Name two common use cases for creating custom JUnit extensions.

Common use cases include managing external resources (like databases or servers) and implementing conditional test execution based on environment or configuration.

Which annotation is used to apply a custom extension to a JUnit 5 test class?

A @UseExtension

B @CustomExtension

C @ExtendWith

D @RegisterExtension

The correct annotation to register a custom extension is @ExtendWith. @RegisterExtension is used for field-level extensions.

Which interface should you implement to run code before all tests in a test class?

A BeforeEachCallback

B TestWatcher

C TestExecutionListener

D BeforeAllCallback

BeforeAllCallback runs code once before all tests. BeforeEachCallback runs before each test.

What does the ExtensionContext NOT provide in a custom extension?

A Ability to modify test source code

B Information about the current test method

C Access to test class instance

D A store to share data between callbacks

ExtensionContext provides test info and data sharing but cannot modify test source code.

How can you share data between different callbacks in a custom extension?

A Using the ExtensionContext's store

B Using static variables

C Using global variables

D Using environment variables

The ExtensionContext provides a Store to safely share data between callbacks.

Which of the following is NOT a typical use case for custom JUnit extensions?

A Conditional test execution

B Changing Java language syntax

C Managing external resources

D Logging test lifecycle events

Custom extensions cannot change Java syntax; they add behavior around tests.

Explain how to create and register a custom extension in JUnit 5.

Think about lifecycle interfaces and how JUnit knows to use your extension.

Describe two practical scenarios where custom JUnit extensions improve testing.

Consider what repetitive tasks or conditions you want to automate in tests.