Flaky test detection in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to mark a test as flaky using JUnit 5.

JUnit

@Test
@[1](5)
void testRandomBehavior() {
    // test code here
}

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

AFlakyTest

BRepeatedTest

CTimeout

DDisabled

Attempts:

3 left

💡 Hint

Common Mistakes

Using @FlakyTest which does not exist in JUnit 5.

Using @Timeout which controls time limits, not repetitions.

JUnit 5 uses @RepeatedTest to run a test multiple times to detect flaky behavior.

2fill in blank

medium

Complete the code to assert that a flaky test passes at least once in multiple runs.

JUnit

int passCount = 0;
for (int i = 0; i < 10; i++) {
    try {
        flakyTest();
        passCount[1];
    } catch (Exception e) {
        // ignore failure
    }
}
assertTrue(passCount > 0);

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

A++

B--

C+=

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '--' which decreases the count.

Using '=' which assigns instead of increments.

Using '++' increments passCount by one each time the test passes.

3fill in blank

hard

Fix the error in the flaky test retry logic by completing the blank.

JUnit

int retries = 3;
while (retries > 0) {
    try {
        flakyTest();
        break;
    } catch (Exception e) {
        retries[1];
        if (retries == 0) throw e;
    }
}

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

A=

B++

C+=

D--

Attempts:

3 left

💡 Hint

Common Mistakes

Using '++' which increases retries causing infinite loop.

Using '=' which assigns instead of decrementing.

Decrement retries with '--' to limit retry attempts.

4fill in blank

hard

Fill both blanks to create a JUnit 5 extension that retries flaky tests up to 3 times.

JUnit

public class RetryExtension implements TestExecutionExceptionHandler {
    private int maxRetries = [1];
    private int retryCount = 0;

    @Override
    public void handleTestExecutionException(ExtensionContext context, Throwable throwable) throws Throwable {
        if (retryCount < maxRetries) {
            retryCount[2];
            context.getRequiredTestMethod().invoke(context.getRequiredTestInstance());
        } else {
            throw throwable;
        }
    }
}

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

A3

B1

C++

D--

Attempts:

3 left

💡 Hint

Common Mistakes

Setting maxRetries to 1 which allows only one attempt.

Decrementing retryCount which causes logic errors.

maxRetries is set to 3 and retryCount is incremented with '++' on each retry.

5fill in blank

hard

Fill all three blanks to implement a flaky test detection method that runs a test 5 times and returns true if it passes at least once.

JUnit

public boolean isFlaky(Runnable test) {
    int passCount = 0;
    for (int i = 0; i < [1]; i++) {
        try {
            test.run();
            passCount [2];
        } catch (Exception e) {
            // ignore failure
        }
    }
    return passCount [3] 0;
}

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

A5

B++

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than '<' instead of greater than '>' in the return statement.

Not incrementing passCount correctly.

Run test 5 times, increment passCount with '++', and check if passCount is greater than 0.