@ValueSource for simple values in JUnit - Build an Automation Script

Test isEven method with multiple integer inputs using @ValueSource

Preconditions (2)

Step 1: Create a parameterized test method using @ValueSource with integers: 2, 4, 6, 8, 10

Step 2: For each integer input, call isEven(number)

Step 3: Verify that the method returns true for all inputs

✅ Expected Result: The test passes confirming isEven returns true for all even numbers provided

Automation Requirements - JUnit 5

Assertions Needed:

Assert that isEven returns true for each input value

Best Practices:

Use @ParameterizedTest with @ValueSource for simple input values

Use descriptive test method names

Keep test methods focused on one behavior

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

Automated Solution

JUnit

import static org.junit.jupiter.api.Assertions.assertTrue;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;

public class NumberUtilsTest {

    // Method to test
    public static boolean isEven(int number) {
        return number % 2 == 0;
    }

    @ParameterizedTest
    @ValueSource(ints = {2, 4, 6, 8, 10})
    void testIsEvenWithEvenNumbers(int number) {
        assertTrue(isEven(number), "Number " + number + " should be even");
    }
}

The test class NumberUtilsTest contains the method isEven which returns true if the number is even.

The test method testIsEvenWithEvenNumbers is annotated with @ParameterizedTest and @ValueSource to run the test multiple times with different integer inputs.

For each input, the test asserts that isEven returns true, confirming the method works correctly for even numbers.

This approach avoids writing multiple test methods for each input and keeps tests clean and readable.

Common Mistakes - 3 Pitfalls

Using @Test instead of @ParameterizedTest for multiple inputs

Passing values as strings instead of correct type in @ValueSource

Not asserting the expected result inside the test method

Bonus Challenge

Now add data-driven testing with 3 different inputs including even and odd numbers and verify isEven returns correct boolean

Show Hint

Practice

1. What is the main purpose of using @ValueSource in JUnit tests?

easy

A. To run the same test multiple times with different simple input values

B. To create a new test class automatically

C. To skip tests based on conditions

D. To generate random test data during runtime

Solution

1. Step 1: Understand the role of @ValueSource

   @ValueSource provides a list of simple values to run a test repeatedly with each value.

2. Step 2: Compare options with this role

   Only To run the same test multiple times with different simple input values correctly describes running the same test multiple times with different inputs.

3. Final Answer:

   To run the same test multiple times with different simple input values -> Option A

4. Quick Check:

   @ValueSource = run test multiple times [OK]

Hint: Remember: @ValueSource repeats tests with simple inputs [OK]

Common Mistakes:

• Thinking @ValueSource creates new test classes
• Confusing @ValueSource with conditional test skipping
• Assuming it generates random data

2. Which of the following is the correct syntax to use @ValueSource with integers in JUnit 5?

easy

A. @ValueSource(numbers = {1, 2, 3})

B. @ValueSource(values = {1, 2, 3})

C. @ValueSource(int = {1, 2, 3})

D. @ValueSource(ints = {1, 2, 3})

Solution

1. Step 1: Recall correct attribute name for integers

   The attribute for integer arrays in @ValueSource is ints.

2. Step 2: Check syntax correctness

   @ValueSource(ints = {1, 2, 3}) uses @ValueSource(ints = {1, 2, 3}), which is the correct syntax.

3. Final Answer:

   @ValueSource(ints = {1, 2, 3}) -> Option D

4. Quick Check:

   ints attribute = correct syntax [OK]

Hint: Use 'ints' attribute for integer arrays in @ValueSource [OK]

Common Mistakes:

• Using wrong attribute names like 'values' or 'numbers'
• Missing 's' in 'ints'
• Using singular 'int' instead of 'ints'

3. Given the following test method, what will be the output when run?

@ParameterizedTest
@ValueSource(strings = {"apple", "banana"})
void testLength(String fruit) {
    System.out.println(fruit.length());
}

medium

A. 5 and 6 printed on separate lines

B. 6 and 5 printed on separate lines

C. Only 5 printed once

D. Compilation error due to missing annotation

Solution

1. Step 1: Identify input values from @ValueSource

   The strings are "apple" (length 5) and "banana" (length 6).

2. Step 2: Understand test execution

   The test runs twice, printing the length of each string in order: 5 then 6.

3. Final Answer:

   5 and 6 printed on separate lines -> Option A

4. Quick Check:

   "apple"=5, "banana"=6 [OK]

Hint: Check string lengths in order given by @ValueSource [OK]

Common Mistakes:

• Mixing order of outputs
• Assuming only one run instead of multiple
• Forgetting @ParameterizedTest annotation

4. Identify the error in this JUnit 5 test using @ValueSource:

@ParameterizedTest
@ValueSource(strings = {"test", null})
void testNotNull(String input) {
    assertNotNull(input);
}

medium

A. Missing @Test annotation

B. assertNotNull is not a valid assertion

C. Using null in @ValueSource causes a runtime error

D. Strings array must not contain more than one value

Solution

1. Step 1: Check @ValueSource limitations

   @ValueSource does not support null values; including null causes errors.

2. Step 2: Verify other parts

   assertNotNull is valid, @ParameterizedTest is present, and multiple strings are allowed.

3. Final Answer:

   Using null in @ValueSource causes a runtime error -> Option C

4. Quick Check:

   null not allowed in @ValueSource [OK]

Hint: Never put null in @ValueSource arrays [OK]

Common Mistakes:

• Thinking null is allowed in @ValueSource
• Confusing @ParameterizedTest with @Test
• Believing assertNotNull is invalid

5. How can you use @ValueSource to test a method that accepts both int and long values?

hard

A. Use @ValueSource with ints only and cast to long inside the test

B. Use two separate test methods each with @ValueSource for ints and longs

C. Use @ValueSource with longs only and cast to int inside the test

D. Use @ValueSource with mixed int and long arrays in one method

Solution

1. Step 1: Understand @ValueSource type restrictions

   @ValueSource attributes accept only one primitive type array per annotation (ints or longs, not mixed).

2. Step 2: Choose approach to test both types

   To test both int and long inputs, create two test methods each with its own @ValueSource for the correct type.

3. Final Answer:

   Use two separate test methods each with @ValueSource for ints and longs -> Option B

4. Quick Check:

   Separate methods for int and long [OK]

Hint: Use separate tests for different primitive types [OK]

Common Mistakes:

• Trying to mix int and long in one @ValueSource
• Casting inside test instead of separate methods
• Assuming @ValueSource supports mixed types