@Test annotation in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the @Test annotation in JUnit?

The @Test annotation marks a method as a test method that JUnit will run automatically during testing.

beginner

Can a method without @Test annotation be run as a test in JUnit?

No, only methods annotated with @Test are recognized and run as tests by JUnit.

intermediate

How do you indicate that a test method is expected to throw an exception using @Test?

You add the expected parameter to @Test, for example: @Test(expected = IllegalArgumentException.class).

beginner

What happens if a test method annotated with @Test fails an assertion?

JUnit marks the test as failed and reports the failure in the test results.

intermediate

Is it possible to run a test method multiple times automatically using @Test alone?

No, @Test alone does not support running a test multiple times. You need additional tools or annotations like @RepeatedTest in JUnit 5.

What does the @Test annotation do in JUnit?

A Marks a method to run before all tests

B Marks a method to be ignored

C Marks a method as private

D Marks a method to be run as a test

@Test tells JUnit to run the method as a test.

How do you specify that a test should expect an exception using @Test?

A Use <code>@Test(expected = Exception.class)</code>

B Use <code>@Test(timeout = 1000)</code>

C Use <code>@Test(ignore = true)</code>

D Use <code>@Test(repeat = 3)</code>

The expected parameter defines the exception the test should expect.

If a method is not annotated with @Test, what happens when you run JUnit tests?

A The method runs as a test anyway

B The method is not run as a test

C JUnit throws an error

D The method runs before tests

Only methods with @Test are run as tests.

What is the default behavior if a test method annotated with @Test throws no exception and all assertions pass?

A Test passes

B Test fails

C Test is ignored

D Test is skipped

If no exceptions occur and assertions pass, the test passes.

Which JUnit annotation is used to run a test multiple times, not @Test?

A <code>@Test(repeat = 3)</code>

B <code>@TestMultiple</code>

C <code>@RepeatedTest</code>

D <code>@RunMultiple</code>

@RepeatedTest is used in JUnit 5 to run tests multiple times.

Explain the role of the @Test annotation in JUnit testing.

Think about how JUnit knows which methods to test.

Describe how you can use the @Test annotation to check if a method throws an expected exception.

Focus on the parameters inside the annotation.

Practice

1. What is the main purpose of the @Test annotation in JUnit?

easy

A. To mark a method as a test case that JUnit will run

B. To declare a method as private

C. To specify the return type of a method

D. To import JUnit libraries

Solution

1. Step 1: Understand the role of @Test

   The @Test annotation tells JUnit which methods are test cases to execute.

2. Step 2: Eliminate unrelated options

   Options B, C, and D do not relate to marking test methods.

3. Final Answer:

   To mark a method as a test case that JUnit will run -> Option A

4. Quick Check:

   @Test marks test methods [OK]

Hint: Remember: @Test means 'run this method as test' [OK]

Common Mistakes:

• Thinking @Test changes method visibility
• Confusing @Test with import statements
• Assuming @Test sets return type

2. Which of the following is the correct syntax for a JUnit test method using @Test?

easy

A. public void testMethod(int x) {}

B. private int testMethod() {}

C. public void testMethod() {}

D. public String testMethod() {}

Solution

1. Step 1: Recall JUnit test method rules

   Test methods must be public, return void, and take no parameters.

2. Step 2: Check each option

   public void testMethod() {} matches all rules. Options B, C, and D violate visibility, return type, or parameters.

3. Final Answer:

   public void testMethod() {} -> Option C

4. Quick Check:

   Public, void, no params = correct test method [OK]

Hint: Test methods: public + void + no parameters [OK]

Common Mistakes:

• Making test methods private
• Adding parameters to test methods
• Using non-void return types

3. Given the code below, what will be the test result when running with JUnit?

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

public class SampleTest {
    @Test
    public void checkSum() {
        int result = 2 + 3;
        assertEquals(5, result);
    }
}

medium

A. Runtime exception thrown

B. Test passes successfully

C. Compilation error due to missing return

D. Test fails with assertion error

Solution

1. Step 1: Analyze the test method logic

   The method calculates 2 + 3 and stores in result, then asserts result equals 5.

2. Step 2: Check assertion correctness

   Since 2 + 3 is 5, the assertion assertEquals(5, result) will pass.

3. Final Answer:

   Test passes successfully -> Option B

4. Quick Check:

   2 + 3 = 5, assertion true [OK]

Hint: If assertion matches calculation, test passes [OK]

Common Mistakes:

• Assuming test fails without checking assertion
• Confusing compilation errors with test failures
• Ignoring that test methods return void

4. Identify the error in the following JUnit test method:

import org.junit.jupiter.api.Test;

public class ErrorTest {
    @Test
    private void testHidden() {
        // test code
    }
}

medium

A. Test method must be public, not private

B. Missing return statement in test method

C. Test method should have parameters

D. Missing @BeforeEach annotation

Solution

1. Step 1: Check method visibility

   JUnit requires test methods to be public so it can access and run them.

2. Step 2: Validate other method properties

   Test methods must be void and parameterless; private visibility is the error here.

3. Final Answer:

   Test method must be public, not private -> Option A

4. Quick Check:

   Test methods must be public [OK]

Hint: Test methods must be public, not private [OK]

Common Mistakes:

• Making test methods private
• Adding parameters to test methods
• Confusing lifecycle annotations with test method requirements

5. You want to write a JUnit test method that checks if a method throws an exception. Which is the correct way to use @Test for this purpose in JUnit 5?

hard

A. Use @Test(expected = Exception.class) annotation parameter

B. Add throws Exception to the test method signature

C. Write a try-catch block without @Test

D. Use @Test with assertThrows() inside the method

Solution

1. Step 1: Recall JUnit 5 exception testing

   JUnit 5 uses assertThrows() inside @Test methods to check exceptions.

2. Step 2: Eliminate outdated or incorrect options

   Use @Test(expected = Exception.class) annotation parameter is from JUnit 4 and invalid in JUnit 5. Add throws Exception to the test method signature only declares exception, not tests it. Write a try-catch block without @Test misses @Test.

3. Final Answer:

   Use @Test with assertThrows() inside the method -> Option D

4. Quick Check:

   JUnit 5 uses assertThrows() inside @Test [OK]

Hint: JUnit 5 tests exceptions with assertThrows() inside @Test [OK]

Common Mistakes:

• Using JUnit 4 style @Test(expected=) in JUnit 5
• Only declaring throws without assertion
• Not using @Test annotation