Why parameterization reduces test duplication in JUnit - Automation Benefits in Action

Verify login functionality with multiple user credentials using parameterization

Preconditions (2)

Step 1: Open the login page

Step 2: Enter username from the test data

Step 3: Enter password from the test data

Step 4: Click the login button

Step 5: Verify that the user is redirected to the dashboard page

✅ Expected Result: User is successfully logged in and redirected to the dashboard page for each set of credentials

Automation Requirements - JUnit 5

Assertions Needed:

Verify the current URL is the dashboard URL after login

Verify no error message is displayed after login

Best Practices:

Use @ParameterizedTest with @CsvSource for input data

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

Keep test method focused on one behavior

Avoid hardcoding test data inside the test method

Automated Solution

JUnit

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

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.CsvSource;
import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;

public class LoginTest {

    WebDriver driver;

    @ParameterizedTest
    @CsvSource({
        "[e-mail], Password1",
        "[e-mail], Password2",
        "[e-mail], Password3"
    })
    void testLoginWithMultipleUsers(String username, String password) {
        driver = new ChromeDriver();
        try {
            driver.get("http://example.com/login");

            driver.findElement(By.id("email")).sendKeys(username);
            driver.findElement(By.id("password")).sendKeys(password);
            driver.findElement(By.id("loginButton")).click();

            // Wait for redirection - simple implicit wait or explicit wait can be used
            Thread.sleep(2000); // For simplicity here, better to use explicit wait in real tests

            String currentUrl = driver.getCurrentUrl();
            assertEquals("http://example.com/dashboard", currentUrl, "User should be redirected to dashboard");

            boolean errorDisplayed = driver.findElements(By.id("loginError")).size() > 0;
            assertFalse(errorDisplayed, "No error message should be displayed after successful login");

        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            driver.quit();
        }
    }
}

This test uses JUnit 5's @ParameterizedTest with @CsvSource to run the same login test with different username and password combinations.

Each test iteration opens the login page, enters the provided credentials, clicks login, and verifies the user is redirected to the dashboard URL.

Assertions check the URL and that no error message is shown.

Parameterization reduces duplication by avoiding writing separate test methods for each user credential set.

The try-finally block ensures the browser closes after each test run.

Note: Thread.sleep is used here for simplicity but explicit waits are recommended in real tests.

Common Mistakes - 4 Pitfalls

Writing separate test methods for each set of credentials

Hardcoding test data inside the test method body

Not closing the browser after each test iteration

Using Thread.sleep instead of explicit waits

Bonus Challenge

Now add data-driven testing with 3 different inputs using @MethodSource instead of @CsvSource

Show Hint

Practice

1. Why does parameterization in JUnit help reduce test duplication?

easy

A. It allows running the same test method multiple times with different inputs.

B. It automatically fixes bugs in the test code.

C. It generates random test data for each test run.

D. It merges multiple test classes into one.

Solution

1. Step 1: Understand parameterization purpose

   Parameterization runs the same test method repeatedly with different input values.

2. Step 2: Compare with duplication

   This avoids writing separate test methods for each input, reducing repeated code.

3. Final Answer:

   It allows running the same test method multiple times with different inputs. -> Option A

4. Quick Check:

   Parameterization = multiple inputs, one test method [OK]

Hint: Parameterization runs one test many times with different data [OK]

Common Mistakes:

• Thinking parameterization fixes bugs automatically
• Confusing parameterization with random data generation
• Believing it merges test classes

2. Which of the following is the correct JUnit 5 syntax to create a parameterized test method?

easy

A. @Test
@ValueSource(strings = {"apple", "banana"})
void testFruit(String fruit) { }

B. @ParameterizedTest
@ValueSource(strings = {"apple", "banana"})
void testFruit(String fruit) { }

C. @Test
@Parameters({"apple", "banana"})
void testFruit(String fruit) { }

D. @ParameterizedTest
@TestSource(strings = {"apple", "banana"})
void testFruit(String fruit) { }

Solution

1. Step 1: Identify correct annotation for parameterized tests

   JUnit 5 uses @ParameterizedTest to mark parameterized test methods.

2. Step 2: Check data source annotation

   @ValueSource provides input values; it must be combined with @ParameterizedTest.

3. Final Answer:

   @ParameterizedTest with @ValueSource is correct syntax. -> Option B

4. Quick Check:

   @ParameterizedTest + @ValueSource = correct syntax [OK]

Hint: Use @ParameterizedTest with @ValueSource for parameterized tests [OK]

Common Mistakes:

• Using @Test instead of @ParameterizedTest
• Using non-existent @Parameters or @TestSource annotations
• Mixing annotations incorrectly

3. Given the following JUnit 5 parameterized test, what will be the output when running the test?

@ParameterizedTest
@ValueSource(ints = {2, 4, 6})
void testIsEven(int number) {
    assertTrue(number % 2 == 0);
}

medium

A. Some tests pass and some fail depending on the number.

B. All tests fail because the assertion is incorrect.

C. All tests pass because all numbers are even.

D. Test will not run due to syntax error.

Solution

1. Step 1: Analyze input values

   The input values are 2, 4, and 6, all even numbers.

2. Step 2: Check assertion logic

   The assertion checks if number % 2 == 0, which is true for all inputs.

3. Final Answer:

   All tests pass because all numbers are even. -> Option C

4. Quick Check:

   All inputs even -> assertion true -> tests pass [OK]

Hint: Check if all inputs satisfy the assertion condition [OK]

Common Mistakes:

• Assuming some numbers are odd without checking
• Confusing assertion logic
• Thinking syntax error exists when it does not

4. Identify the error in this JUnit 5 parameterized test code:

@ParameterizedTest
@ValueSource(strings = {"test", "JUnit"})
void testLength(int length) {
    assertTrue(length > 0);
}

medium

A. assertTrue cannot be used in parameterized tests.

B. The @ValueSource annotation is missing parentheses.

C. The test method must return a value.

D. The parameter type should be String, not int.

Solution

1. Step 1: Check parameter type against @ValueSource data

   @ValueSource provides strings, but method parameter is int, causing a type mismatch.

2. Step 2: Understand correct parameter type

   The method parameter should be String to match the input data type.

3. Final Answer:

   The parameter type should be String, not int. -> Option D

4. Quick Check:

   Parameter type must match @ValueSource data type [OK]

Hint: Match method parameter type with @ValueSource data type [OK]

Common Mistakes:

• Using wrong parameter type
• Forgetting parentheses in annotations (not the case here)
• Thinking test methods must return values
• Believing assertTrue is disallowed in parameterized tests

5. You have multiple test methods checking if numbers are positive, negative, or zero. How does parameterization reduce duplication in this scenario?

hard

A. By combining all checks into one parameterized test method with input and expected result parameters.

B. By writing separate test classes for each number type.

C. By removing assertions and relying on manual checks.

D. By running tests only once with a fixed number.

Solution

1. Step 1: Understand test duplication problem

   Multiple test methods for positive, negative, zero numbers cause repeated code.

2. Step 2: Apply parameterization to combine tests

   Use one parameterized test method with inputs and expected results to cover all cases.

3. Final Answer:

   By combining all checks into one parameterized test method with input and expected result parameters. -> Option A

4. Quick Check:

   One method + multiple inputs = less duplication [OK]

Hint: Use one test method with inputs and expected outputs [OK]

Common Mistakes:

• Writing separate test classes instead of parameterizing
• Removing assertions which breaks test automation
• Testing only one fixed input