@Test annotation in JUnit - Build an Automation Script

Verify addition method returns correct sum

Preconditions (2)

Step 1: Create a test class named CalculatorTest

Step 2: Write a test method named testAdd annotated with @Test

Step 3: Inside testAdd, call Calculator.add(2, 3)

Step 4: Assert that the result equals 5

✅ Expected Result: The test passes confirming that add(2, 3) returns 5

Automation Requirements - JUnit 5

Assertions Needed:

Assert that Calculator.add(2, 3) returns 5

Best Practices:

Use @Test annotation on test methods

Use meaningful method names

Use assertions from org.junit.jupiter.api.Assertions

Keep test methods independent and simple

Automated Solution

JUnit

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

class Calculator {
    public static int add(int a, int b) {
        return a + b;
    }
}

public class CalculatorTest {
    @Test
    void testAdd() {
        int result = Calculator.add(2, 3);
        assertEquals(5, result, "2 + 3 should equal 5");
    }
}

The @Test annotation marks the method testAdd as a test method for JUnit to run.

Inside testAdd, we call the add method from the Calculator class with inputs 2 and 3.

We then use assertEquals to check if the result is 5. If it is, the test passes; otherwise, it fails.

This simple structure shows how @Test helps JUnit identify and run test methods automatically.

Common Mistakes - 3 Pitfalls

Forgetting to annotate the test method with @Test

Using assert statements from java.lang instead of JUnit assertions

Naming test methods without descriptive names

Bonus Challenge

Now add data-driven testing with 3 different input pairs for the add method

Show Hint

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