Multiple parameter types in JUnit - Build an Automation Script

Verify addition method with multiple parameter types

Preconditions (1)

Step 1: Call the add method with integer 5 and double 3.2

Step 2: Call the add method with integer -1 and double 0.0

Step 3: Call the add method with integer 0 and double -2.5

✅ Expected Result: The add method returns the correct sum as double for each pair of inputs: 8.2, -1.0, and -2.5 respectively.

Automation Requirements - JUnit 5

Assertions Needed:

Assert that the returned value is equal to the expected sum with a small delta for floating point comparison.

Best Practices:

Use @ParameterizedTest with @MethodSource to supply multiple parameter types

Use descriptive test method names

Use assertions with delta for double comparison

Keep test code clean and readable

Automated Solution

JUnit

import static org.junit.jupiter.api.Assertions.assertEquals;
import java.util.stream.Stream;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.MethodSource;

public class CalculatorTest {

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

    private static Stream<org.junit.jupiter.params.provider.Arguments> provideParameters() {
        return Stream.of(
            org.junit.jupiter.params.provider.Arguments.of(5, 3.2, 8.2),
            org.junit.jupiter.params.provider.Arguments.of(-1, 0.0, -1.0),
            org.junit.jupiter.params.provider.Arguments.of(0, -2.5, -2.5)
        );
    }

    @ParameterizedTest(name = "add({0}, {1}) = {2}")
    @MethodSource("provideParameters")
    void testAddWithMultipleParameterTypes(int a, double b, double expected) {
        Calculator calculator = new Calculator();
        double result = calculator.add(a, b);
        assertEquals(expected, result, 0.0001, "Sum should be correct");
    }
}

This test uses JUnit 5's @ParameterizedTest with @MethodSource to supply multiple sets of parameters with different types: an int and a double. The Calculator class has an add method that takes these two parameters and returns their sum as a double.

The provideParameters method returns a stream of arguments with three test cases. The test method testAddWithMultipleParameterTypes receives these parameters, calls the add method, and asserts the result is equal to the expected sum using assertEquals with a small delta to handle floating point precision.

This approach keeps the test clean, readable, and easily extendable for more cases.

Common Mistakes - 3 Pitfalls

Using @ValueSource which supports only one parameter type

Not using delta in assertEquals for double comparison

Hardcoding test data inside the test method instead of using parameterized tests

Bonus Challenge

Now add data-driven testing with 3 different inputs including zero and negative values

Show Hint

Practice

1. What is the main benefit of using @ParameterizedTest with multiple parameter types in JUnit?

easy

A. It makes tests run faster by skipping assertions.

B. It automatically fixes bugs in the tested code.

C. It allows running the same test method with different input values easily.

D. It generates test reports without writing any code.

Solution

1. Step 1: Understand the purpose of @ParameterizedTest

   @ParameterizedTest lets you run one test method multiple times with different inputs.

2. Step 2: Recognize the benefit of multiple parameter types

   Using multiple parameter types means you can test various input combinations easily, improving coverage.

3. Final Answer:

   It allows running the same test method with different input values easily. -> Option C

4. Quick Check:

   @ParameterizedTest runs tests with many inputs = A [OK]

Hint: Think: same test, many inputs, easy coverage [OK]

Common Mistakes:

• Confusing parameterized tests with automatic bug fixing
• Believing it skips assertions to run faster
• Assuming it generates reports without code

2. Which of the following is the correct syntax to provide multiple parameters of different types using @CsvSource in JUnit?

easy

A. @CsvSource({"1, 'test', true", "2, 'check', false"})

B. @CsvSource(1, 'test', true; 2, 'check', false)

C. @CsvSource([1, 'test', true], [2, 'check', false])

D. @CsvSource("1; 'test'; true", "2; 'check'; false")

Solution

1. Step 1: Recall the correct @CsvSource format

   @CsvSource expects an array of strings, each string with comma-separated values.

2. Step 2: Check each option's syntax

   @CsvSource({"1, 'test', true", "2, 'check', false"}) uses curly braces and comma-separated values inside quotes, which is correct syntax.

3. Final Answer:

   @CsvSource({"1, 'test', true", "2, 'check', false"}) -> Option A

4. Quick Check:

   @CsvSource uses braces and comma-separated strings = C [OK]

Hint: Look for braces and comma-separated quoted strings [OK]

Common Mistakes:

• Using semicolons instead of commas
• Not enclosing the whole list in braces
• Using square brackets instead of braces

3. Given the following JUnit test method, what will be the output when it runs?

@ParameterizedTest
@CsvSource({"2, 3, 5", "4, 5, 9", "1, 1, 3"})
void testSum(int a, int b, int expected) {
    assertEquals(expected, a + b);
}

medium

A. Syntax error prevents tests from running.

B. All tests pass.

C. All tests fail.

D. Two tests pass, one test fails.

Solution

1. Step 1: Check each test case's expected vs actual sum

   Test 1: 2+3=5 matches expected 5 (pass). Test 2: 4+5=9 matches expected 9 (pass). Test 3: 1+1=2 but expected 3 (fail).

2. Step 2: Determine overall test results

   Two tests pass, one test fails due to wrong expected value.

3. Final Answer:

   Two tests pass, one test fails. -> Option D

4. Quick Check:

   Sum matches expected except last = A [OK]

Hint: Add inputs and compare to expected for each case [OK]

Common Mistakes:

• Assuming all pass without checking expected values
• Ignoring the failing test case
• Thinking syntax error occurs due to quotes

4. Identify the error in this JUnit parameterized test using multiple parameter types:

@ParameterizedTest
@CsvSource({"10, 20", "30, 40"})
void testMultiply(int a, int b, int expected) {
    assertEquals(expected, a * b);
}

medium

A. The @CsvSource syntax is incorrect; it should use semicolons instead of commas.

B. The method expects three parameters but only two are provided in @CsvSource.

C. The assertEquals arguments are reversed.

D. The test method should not use @ParameterizedTest with @CsvSource.

Solution

1. Step 1: Compare method parameters with @CsvSource values

   The method expects three parameters (int a, int b, int expected), but each @CsvSource entry has only two values.

2. Step 2: Identify mismatch causing error

   Missing the third parameter in @CsvSource causes a runtime error due to parameter count mismatch.

3. Final Answer:

   The method expects three parameters but only two are provided in @CsvSource. -> Option B

4. Quick Check:

   Parameter count mismatch = B [OK]

Hint: Count parameters in method and CsvSource entries [OK]

Common Mistakes:

• Thinking commas are wrong separators
• Assuming assertEquals argument order causes error
• Believing @ParameterizedTest can't be used with @CsvSource

5. You want to test a method isValidUser(String username, int age, boolean active) using @ParameterizedTest with multiple parameter types. Which @CsvSource entry correctly represents a test case with username "alice", age 30, and active status true?

hard

A. "alice, 30, true"

B. "'alice', 30, true"

C. "alice; 30; true"

D. "alice, '30', 'true'"

Solution

1. Step 1: Understand @CsvSource value format

   Values are comma-separated strings; quotes around strings are optional unless spaces or commas inside.

2. Step 2: Evaluate each option

   "alice, 30, true" correctly uses commas without extra quotes. "'alice', 30, true" adds unnecessary quotes around username. "alice; 30; true" uses semicolons which is invalid. "alice, '30', 'true'" quotes numeric and boolean values unnecessarily.

3. Final Answer:

   "alice, 30, true" -> Option A

4. Quick Check:

   Comma-separated values without extra quotes = D [OK]

Hint: Use commas, quote strings only if needed [OK]

Common Mistakes:

• Using semicolons instead of commas
• Adding quotes around numbers or booleans
• Quoting strings unnecessarily