Parallel test configuration in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

JUnit Parallel Execution Output

Given the following JUnit 5 test class configured to run tests in parallel, what will be the output order of the test methods?

JUnit

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.parallel.Execution;
import org.junit.jupiter.api.parallel.ExecutionMode;

@Execution(ExecutionMode.CONCURRENT)
public class ParallelTest {

    @Test
    void testA() throws InterruptedException {
        Thread.sleep(100);
        System.out.println("A");
    }

    @Test
    void testB() {
        System.out.println("B");
    }

    @Test
    void testC() throws InterruptedException {
        Thread.sleep(50);
        System.out.println("C");
    }
}

A B, C, A

B A, B, C

C C, B, A

D B, A, C

💡 Hint

Consider that tests run concurrently and sleep delays affect output timing.

Since testB has no delay, it prints immediately. testC sleeps 50ms, testA sleeps 100ms. So output order is B, then C, then A.

❓ assertion

intermediate

Correct Assertion for Parallel Test Count

In a JUnit 5 test suite configured with junit.jupiter.execution.parallel.enabled = true and junit.jupiter.execution.parallel.config.fixed.parallelism = 3, which assertion correctly verifies that exactly 3 tests run in parallel?

A assertTrue(parallelismLevel >= 3);

B assertNotNull(parallelismLevel);

C assertFalse(parallelismLevel > 3);

D assertEquals(3, parallelismLevel);

💡 Hint

The fixed parallelism config sets the exact number of parallel threads.

The fixed.parallelism property sets the exact number of threads, so the assertion must check equality to 3.

🔧 Debug

advanced

Debugging Parallel Test Failures

A JUnit 5 test suite runs tests in parallel but intermittently fails due to shared resource conflicts. Which change best fixes this issue?

A Remove <code>@Execution(ExecutionMode.CONCURRENT)</code> to run tests sequentially.

B Increase <code>fixed.parallelism</code> to reduce test overlap.

C Add <code>@ResourceLock("sharedResource")</code> to tests accessing the resource.

D Use <code>@TestInstance(Lifecycle.PER_CLASS)</code> to share state across tests.

💡 Hint

JUnit 5 provides annotations to control resource locking in parallel tests.

Using @ResourceLock ensures tests accessing the same resource do not run simultaneously, preventing conflicts.

❓ framework

advanced

JUnit 5 Parallel Execution Configuration

Which configuration snippet correctly enables parallel test execution with a fixed thread pool of 4 threads in JUnit 5?

A

junit.jupiter.execution.parallel.enabled = false
junit.jupiter.execution.parallel.config.strategy = fixed
junit.jupiter.execution.parallel.config.fixed.parallelism = 4

B

junit.jupiter.execution.parallel.enabled = true
junit.jupiter.execution.parallel.config.strategy = fixed
junit.jupiter.execution.parallel.config.fixed.parallelism = 4

C

junit.jupiter.execution.parallel.enabled = true
junit.jupiter.execution.parallel.config.strategy = dynamic
junit.jupiter.execution.parallel.config.fixed.parallelism = 4

D

junit.jupiter.execution.parallel.enabled = true
junit.jupiter.execution.parallel.config.strategy = fixed
junit.jupiter.execution.parallel.config.fixed.parallelism = 2

💡 Hint

Parallel execution must be enabled and strategy set to fixed with desired parallelism.

Option B correctly enables parallel execution with fixed strategy and sets parallelism to 4 threads.

🧠 Conceptual

expert

Impact of Parallel Test Execution on Test Isolation

Which statement best describes the impact of enabling parallel test execution in JUnit 5 on test isolation?

A Parallel execution can cause shared mutable state issues unless tests are designed for isolation.

B Parallel execution guarantees complete test isolation by default.

C JUnit 5 disables static variables when parallel execution is enabled to ensure isolation.

D Tests running in parallel always share the same instance, so isolation is not possible.

💡 Hint

Think about how shared data affects tests running at the same time.

Parallel execution runs tests concurrently, so if tests share mutable state without proper isolation, conflicts can occur.