TestInstance lifecycle per class in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the @TestInstance(Lifecycle.PER_CLASS) annotation do in JUnit?

It tells JUnit to create only one instance of the test class and reuse it for all test methods, instead of creating a new instance for each test method.

intermediate

Why might you use @TestInstance(Lifecycle.PER_CLASS) instead of the default lifecycle?

To share state or expensive setup between test methods, reducing repeated initialization and improving test performance.

intermediate

How does @BeforeAll behave differently when using @TestInstance(Lifecycle.PER_CLASS)?

With PER_CLASS lifecycle, <code>@BeforeAll</code> methods can be non-static because the same test instance is reused.

beginner

What is the default test instance lifecycle in JUnit 5?

The default lifecycle is <code>PER_METHOD</code>, which creates a new test class instance for each test method.

advanced

What is a potential risk of using @TestInstance(Lifecycle.PER_CLASS)?

Tests might become dependent on each other if shared state is modified, leading to flaky or unreliable tests.

What happens when you annotate a JUnit 5 test class with @TestInstance(Lifecycle.PER_CLASS)?

A JUnit creates a new instance for each test method.

B JUnit creates one instance of the test class for all tests.

C JUnit disables all tests in the class.

D JUnit runs tests in parallel automatically.

PER_CLASS lifecycle means one instance is reused for all test methods.

Which method can be non-static when using @TestInstance(Lifecycle.PER_CLASS)?

A <code>@BeforeAll</code>

B <code>@AfterEach</code>

C <code>@Test</code>

D <code>@BeforeEach</code>

With PER_CLASS, @BeforeAll can be non-static because the same instance is used.

What is the default lifecycle of test instances in JUnit 5?

A PER_CLASS

B PER_TEST

C PER_SUITE

D PER_METHOD

JUnit 5 creates a new instance per test method by default (PER_METHOD).

What is a common reason to choose PER_CLASS lifecycle?

A To isolate tests completely

B To run tests faster by skipping assertions

C To share expensive setup across tests

D To disable test methods selectively

PER_CLASS allows sharing setup or state to improve performance.

What risk does PER_CLASS lifecycle introduce?

A Tests may become dependent on shared state

B Tests run slower

C Tests cannot use <code>@BeforeAll</code>

D JUnit throws errors on multiple test methods

Shared state can cause tests to affect each other, leading to flaky tests.

Explain how the @TestInstance(Lifecycle.PER_CLASS) annotation changes the lifecycle of test instances in JUnit 5.

Think about how many times the test class is created.

Describe the benefits and risks of using the PER_CLASS lifecycle in JUnit testing.

Consider both positive and negative effects on test design.