First JUnit test - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the JUnit test annotation.

JUnit

import org.junit.jupiter.api.[1];

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

AAfterAll

BBeforeEach

CDisabled

DTest

Attempts:

3 left

💡 Hint

Common Mistakes

Importing other annotations like BeforeEach instead of Test.

Forgetting to import any annotation.

The @Test annotation marks a method as a test method in JUnit 5.

2fill in blank

medium

Complete the code to write a simple test method named testAddition.

JUnit

@Test
public void [1]() {
    int sum = 2 + 3;
    org.junit.jupiter.api.Assertions.assertEquals(5, sum);
}

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

AtestAddition

BcheckSum

CadditionTest

DsumTest

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name than requested.

Forgetting the @Test annotation.

The test method should be named testAddition as requested.

3fill in blank

hard

Fix the error in the assertion to correctly check that result equals 10.

JUnit

int result = 5 + 5;
org.junit.jupiter.api.Assertions.assertEquals([1], result);

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

A10

B5 + 5

C"10"

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Using the variable result as expected value.

Using a string "10" instead of integer 10.

The expected value should be the integer 10, not a string or variable.

4fill in blank

hard

Fill both blanks to create a test method that checks if multiply(2, 3) returns 6.

JUnit

@Test
public void [1]() {
    int output = multiply(2, 3);
    org.junit.jupiter.api.Assertions.[2](6, output);
}

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

AtestMultiply

BassertEquals

CassertTrue

DmultiplyTest

Attempts:

3 left

💡 Hint

Common Mistakes

Using assertTrue instead of assertEquals.

Using a wrong method name.

The method name should be testMultiply and the assertion method is assertEquals to compare expected and actual values.

5fill in blank

hard

Fill all three blanks to write a test method that verifies isEven(4) returns true.

JUnit

@Test
public void [1]() {
    boolean result = isEven([2]);
    org.junit.jupiter.api.Assertions.[3](result);
}

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

AtestIsEven

B4

CassertEquals

DassertTrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using assertEquals instead of assertTrue for boolean checks.

Passing wrong input value.

The method name is testIsEven, the input is 4, and the assertion is assertTrue to check the boolean result.

Practice

1. What is the main purpose of a JUnit test method marked with @Test?

easy

A. To check if a piece of code works as expected

B. To create a new Java class

C. To print output to the console

D. To declare a variable

Solution

1. Step 1: Understand the role of @Test annotation

   The @Test annotation marks a method as a test method in JUnit, meaning it will be run to check code behavior.

2. Step 2: Identify the purpose of test methods

   Test methods verify if the code produces the expected results, helping find bugs or confirm correctness.

3. Final Answer:

   To check if a piece of code works as expected -> Option A

4. Quick Check:

   JUnit @Test marks test methods [OK]

Hint: JUnit tests verify code correctness using @Test [OK]

Common Mistakes:

• Thinking @Test creates classes
• Confusing test methods with print statements
• Using @Test to declare variables

2. Which of the following is the correct way to write a simple JUnit 5 test method?

easy

A. public void testMethod() { assertEquals(5, 2 + 3); }

B. void testMethod() { assertEquals(5, 2 + 3); }

C. @Test public void testMethod() { assertEquals(5, 2 + 3); }

D. @Test void testMethod() { System.out.println(5); }

Solution

1. Step 1: Check for @Test annotation

   JUnit 5 requires the @Test annotation to mark a method as a test.

2. Step 2: Verify method signature and assertion

   The method should be public void with an assertion like assertEquals(expected, actual). @Test public void testMethod() { assertEquals(5, 2 + 3); } matches this.

3. Final Answer:

   @Test public void testMethod() { assertEquals(5, 2 + 3); } -> Option C

4. Quick Check:

   JUnit test method needs @Test and assertion [OK]

Hint: Always use @Test before test methods [OK]

Common Mistakes:

• Missing @Test annotation
• Wrong method visibility or return type
• Using print statements instead of assertions

3. What will be the result of running this JUnit test?

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

public class SampleTest {
  @Test
  void additionTest() {
    assertEquals(10, 5 + 5);
  }
}

medium

A. Runtime exception occurs

B. Test passes successfully

C. Compilation error due to missing import

D. Test fails with assertion error

Solution

1. Step 1: Analyze the assertion

   The test asserts that 5 + 5 equals 10, which is true.

2. Step 2: Check for syntax and imports

   All necessary imports and syntax are correct, so the test will run without errors.

3. Final Answer:

   Test passes successfully -> Option B

4. Quick Check:

   Correct assertion means test passes [OK]

Hint: True assertions make tests pass [OK]

Common Mistakes:

• Assuming test fails when assertion is true
• Missing static import for assertions
• Confusing compilation errors with runtime errors

4. Identify the error in this JUnit test code:

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

public class CalcTest {
  @Test
  public void testSum() {
    int result = 2 + 2;
    assertEquals(5, result);
  }
}

medium

A. The assertion expects wrong value causing test failure

B. Missing @Test annotation

C. Method should return int, not void

D. No import for assertEquals

Solution

1. Step 1: Check the assertion values

   The test expects 5 but the actual result is 4 (2 + 2), so the assertion will fail.

2. Step 2: Verify annotations and imports

   The @Test annotation and imports are correct, so no syntax errors exist.

3. Final Answer:

   The assertion expects wrong value causing test failure -> Option A

4. Quick Check:

   Assertion mismatch causes test failure [OK]

Hint: Check expected vs actual values in assertions [OK]

Common Mistakes:

• Ignoring assertion expected value
• Thinking missing annotation causes failure here
• Confusing method return types in tests

5. You want to write a JUnit test that checks if a method multiply(int a, int b) returns 0 when one input is 0. Which test method is correct?

hard

A. @Test public void testMultiplyZero() { assertEquals(5, multiply(0, 5)); }

B. public void testMultiplyZero() { assertEquals(0, multiply(0, 5)); }

C. @Test public int testMultiplyZero() { return multiply(0, 5); }

D. @Test public void testMultiplyZero() { assertEquals(0, multiply(0, 5)); }

Solution

1. Step 1: Confirm @Test annotation and method signature

   The test method must be annotated with @Test and return void. @Test public void testMultiplyZero() { assertEquals(0, multiply(0, 5)); } meets this.

2. Step 2: Check assertion correctness

   The method should assert that multiplying by zero returns zero. @Test public void testMultiplyZero() { assertEquals(0, multiply(0, 5)); } asserts assertEquals(0, multiply(0, 5)), which is correct.

3. Final Answer:

   @Test public void testMultiplyZero() { assertEquals(0, multiply(0, 5)); } -> Option D

4. Quick Check:

   Use @Test, void method, correct assertion [OK]

Hint: Test methods need @Test, void, and correct assertions [OK]

Common Mistakes:

• Omitting @Test annotation
• Using wrong return type in test method
• Asserting wrong expected value