Test execution time analysis in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

JUnit test execution time output

What will be the output of the following JUnit 5 test when run?

JUnit

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

class TimeTest {
    @Test
    void fastTest() throws InterruptedException {
        Thread.sleep(50);
        assertTrue(true);
    }
}

A Test fails due to assertion error

B Test passes instantly with 0 ms execution time

C Test passes with execution time approximately 50 ms

D Test throws InterruptedException and fails

💡 Hint

Thread.sleep pauses the test for the given milliseconds before assertion.

The test sleeps for 50 milliseconds before asserting true, so the test passes and the execution time is about 50 ms.

❓ assertion

intermediate

Assertion to check test execution time under limit

Which assertion correctly verifies that a method completes within 100 milliseconds using JUnit 5?

JUnit

import static org.junit.jupiter.api.Assertions.*;
import java.time.Duration;

// Assume methodToTest() is the method to check

A assertTrue(methodToTest() < 100);

B assertTimeout(Duration.ofMillis(100), () -> methodToTest());

C assertEquals(100, methodToTest());

D assertTimeoutPreemptively(Duration.ofSeconds(1), () -> methodToTest());

💡 Hint

Use JUnit 5's timeout assertions with Duration.

assertTimeout checks that the method completes within the given Duration. Option B uses it correctly with 100 ms.

🔧 Debug

advanced

Identify why test execution time is longer than expected

A JUnit test with Thread.sleep(10) runs for 500 ms instead of about 10 ms. What is the most likely cause?

A The test method contains multiple Thread.sleep calls adding up to 500 ms

B JUnit automatically adds 490 ms delay to all tests

C The test is running on a very slow machine causing Thread.sleep to last longer

D Thread.sleep(10) actually sleeps for 500 ms due to JVM bug

💡 Hint

Check the test code for multiple sleep calls or loops.

Multiple sleep calls or loops with sleep can accumulate to longer total sleep time, causing longer test execution.

🧠 Conceptual

advanced

Understanding impact of test execution time on CI pipelines

Why is it important to monitor and limit test execution time in continuous integration (CI) pipelines?

A To prevent tests from running on developer machines

B To increase the number of tests run in parallel regardless of duration

C To ensure tests always fail if they run longer than 1 second

D To reduce feedback time and improve developer productivity

💡 Hint

Think about how long developers wait for test results.

Shorter test execution times mean faster feedback, helping developers fix issues quickly and maintain productivity.

❓ framework

expert

Configuring JUnit 5 to fail tests exceeding time limit

Which JUnit 5 annotation and parameter combination will cause a test to fail if it runs longer than 200 milliseconds?

A

@Test
@Timeout(value = 200, unit = java.util.concurrent.TimeUnit.MILLISECONDS)
void testMethod() {}

B

@Test
@Timeout(200)
void testMethod() {}

C

@Test
@Timeout(value = 200)
void testMethod() {}

D

@Test
@Timeout(value = 200, unit = java.time.temporal.ChronoUnit.MILLIS)
void testMethod() {}

💡 Hint

Check the correct import and parameter types for @Timeout annotation.

Option A correctly uses @Timeout with value and TimeUnit.MILLISECONDS to fail test if it exceeds 200 ms.