BeforeEachCallback and AfterEachCallback in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to implement a JUnit extension that runs code before each test.

JUnit

public class MyExtension implements BeforeEachCallback {
    @Override
    public void [1](ExtensionContext context) throws Exception {
        System.out.println("Before each test");
    }
}

Drag options to blanks, or click blank then click option'

AbeforeEach

BbeforeAll

CafterEach

DafterAll

Attempts:

3 left

💡 Hint

Common Mistakes

Using afterEach instead of beforeEach

Using beforeAll which runs once before all tests

The method to override in BeforeEachCallback is beforeEach, which runs before each test method.

2fill in blank

medium

Complete the code to implement a JUnit extension that runs code after each test.

JUnit

public class MyExtension implements AfterEachCallback {
    @Override
    public void [1](ExtensionContext context) throws Exception {
        System.out.println("After each test");
    }
}

Drag options to blanks, or click blank then click option'

AbeforeEach

BafterEach

CbeforeAll

DafterAll

Attempts:

3 left

💡 Hint

Common Mistakes

Using beforeEach instead of afterEach

Using afterAll which runs once after all tests

The method to override in AfterEachCallback is afterEach, which runs after each test method.

3fill in blank

hard

Fix the error in the method signature to correctly implement BeforeEachCallback.

JUnit

public class MyExtension implements BeforeEachCallback {
    @Override
    public void [1] {
        System.out.println("Before each test");
    }
}

Drag options to blanks, or click blank then click option'

AafterEach(ExtensionContext context) throws Exception

BbeforeEach()

CbeforeAll(ExtensionContext context)

DbeforeEach(ExtensionContext context) throws Exception

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the ExtensionContext parameter

Not declaring throws Exception

The beforeEach method must accept ExtensionContext and declare throws Exception to correctly override the interface method.

4fill in blank

hard

Fill both blanks to implement a JUnit extension that prints messages before and after each test.

JUnit

public class MyExtension implements BeforeEachCallback, AfterEachCallback {
    @Override
    public void [1](ExtensionContext context) throws Exception {
        System.out.println("Starting test");
    }

    @Override
    public void [2](ExtensionContext context) throws Exception {
        System.out.println("Finished test");
    }
}

Drag options to blanks, or click blank then click option'

AbeforeEach

BafterAll

CafterEach

DbeforeAll

Attempts:

3 left

💡 Hint

Common Mistakes

Using beforeAll or afterAll which run once per test class

Swapping beforeEach and afterEach method names

beforeEach runs before each test, afterEach runs after each test. These are the correct method names for the respective interfaces.

5fill in blank

hard

Fill all three blanks to create a JUnit extension that logs before each test, after each test, and handles exceptions.

JUnit

public class LoggingExtension implements BeforeEachCallback, AfterEachCallback {
    @Override
    public void [1](ExtensionContext context) throws Exception {
        System.out.println("Log start: " + context.getDisplayName());
    }

    @Override
    public void [2](ExtensionContext context) throws Exception {
        System.out.println("Log end: " + context.getDisplayName());
    }

    public void handleException(Throwable [3]) {
        System.out.println("Exception caught: " + [3].getMessage());
    }
}

Drag options to blanks, or click blank then click option'

AbeforeEach

BafterEach

Cex

Dexception

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong method names for the interface methods

Using invalid variable names for the exception parameter

The methods beforeEach and afterEach are from the interfaces. The exception parameter name can be any valid identifier; here 'ex' is used.

Practice

1. What is the main purpose of implementing BeforeEachCallback and AfterEachCallback in JUnit 5?

easy

A. To skip tests based on conditions

B. To run code before and after each test method for setup and cleanup

C. To replace the test methods with custom logic

D. To run code only once before all tests in a class

Solution

1. Step 1: Understand the role of BeforeEachCallback and AfterEachCallback

   These interfaces allow running code before and after each test method, typically for setup and cleanup.

2. Step 2: Compare with other lifecycle callbacks

   Unlike @BeforeAll or @AfterAll, these run before and after every test, not once per class.

3. Final Answer:

   To run code before and after each test method for setup and cleanup -> Option B

4. Quick Check:

   BeforeEachCallback and AfterEachCallback = setup and cleanup per test [OK]

Hint: They run code before and after each test method [OK]

Common Mistakes:

• Confusing with @BeforeAll/@AfterAll which run once per class
• Thinking they replace test methods
• Assuming they skip tests

2. Which method must be implemented when using the BeforeEachCallback interface in JUnit 5?

easy

A. void beforeEach(ExtensionContext context)

B. void beforeAll(ExtensionContext context)

C. void afterEach(ExtensionContext context)

D. void afterAll(ExtensionContext context)

Solution

1. Step 1: Recall the method signature for BeforeEachCallback

   The interface requires implementing beforeEach(ExtensionContext context) to run code before each test.

2. Step 2: Differentiate from other lifecycle methods

   Methods like beforeAll or afterAll belong to other interfaces or annotations, not BeforeEachCallback.

3. Final Answer:

   void beforeEach(ExtensionContext context) -> Option A

4. Quick Check:

   BeforeEachCallback method = beforeEach() [OK]

Hint: BeforeEachCallback requires beforeEach() method [OK]

Common Mistakes:

• Using beforeAll or afterAll methods incorrectly
• Confusing AfterEachCallback method with BeforeEachCallback
• Missing the ExtensionContext parameter

3. Given the following JUnit 5 extension code, what will be printed when running a test method?

public class MyExtension implements BeforeEachCallback, AfterEachCallback {
    @Override
    public void beforeEach(ExtensionContext context) {
        System.out.println("Start " + context.getDisplayName());
    }
    @Override
    public void afterEach(ExtensionContext context) {
        System.out.println("End " + context.getDisplayName());
    }
}

Assuming the test method is named testExample() in class ExampleTest.

medium

A. Start ExampleTest
testExample End

B. Only Start testExample(ExampleTest) is printed

C. testExample Start
ExampleTest End

D. Start testExample(ExampleTest)
End testExample(ExampleTest)

Solution

1. Step 1: Understand what context.getDisplayName() returns

   It returns the display name of the current test, typically in the format "methodName(className)".

2. Step 2: Analyze the print statements in beforeEach and afterEach

   Before the test, it prints "Start " plus the display name; after the test, it prints "End " plus the same display name.

3. Final Answer:

   Start testExample(ExampleTest) End testExample(ExampleTest) -> Option D

4. Quick Check:

   beforeEach prints Start + displayName, afterEach prints End + displayName [OK]

Hint: context.getDisplayName() shows method and class name [OK]

Common Mistakes:

• Assuming displayName returns only class or method name
• Thinking only one print runs
• Mixing order of prints

4. Identify the error in this JUnit 5 extension code implementing AfterEachCallback:

public class CleanupExtension implements AfterEachCallback {
    public void afterEach() {
        System.out.println("Cleaning up after test");
    }
}

medium

A. Class must implement BeforeEachCallback too

B. afterEach method should be static

C. Missing ExtensionContext parameter in afterEach method

D. System.out.println is not allowed in extensions

Solution

1. Step 1: Check method signature for AfterEachCallback

   The interface requires implementing afterEach(ExtensionContext context) with the ExtensionContext parameter.

2. Step 2: Identify the missing parameter error

   The code's afterEach method has no parameters, so it does not correctly override the interface method.

3. Final Answer:

   Missing ExtensionContext parameter in afterEach method -> Option C

4. Quick Check:

   AfterEachCallback.afterEach() requires ExtensionContext parameter [OK]

Hint: Check method parameters match interface exactly [OK]

Common Mistakes:

• Omitting ExtensionContext parameter
• Making method static incorrectly
• Thinking BeforeEachCallback is mandatory
• Believing print statements are disallowed

5. You want to create a JUnit 5 extension that logs the start time before each test and logs the elapsed time after each test. Which approach correctly uses BeforeEachCallback and AfterEachCallback to achieve this?

hard

A. Store start time in a field in beforeEach, then calculate elapsed time in afterEach using the same field

B. Store start time in a local variable inside beforeEach and reuse it in afterEach

C. Use static variables to store start time shared across all tests

D. Only implement BeforeEachCallback and log elapsed time after test in test method

Solution

1. Step 1: Understand lifecycle of BeforeEachCallback and AfterEachCallback

   They run before and after each test method, so storing start time in a field allows sharing data between these callbacks for the same test.

2. Step 2: Evaluate options for storing start time

   Local variables in beforeEach cannot be accessed in afterEach; static variables cause data sharing issues across tests; logging elapsed time in test method breaks separation of concerns.

3. Final Answer:

   Store start time in a field in beforeEach, then calculate elapsed time in afterEach using the same field -> Option A

4. Quick Check:

   Use instance field to share data between beforeEach and afterEach [OK]

Hint: Use instance fields to share data between callbacks [OK]

Common Mistakes:

• Trying to share data via local variables
• Using static fields causing test interference
• Logging elapsed time inside test methods