Parameterized Unit Tests with JUnit 5

Overview

Provides patterns for parameterized unit tests in Java using JUnit 5. Covers @ValueSource , @CsvSource , @MethodSource , @EnumSource , @ArgumentsSource , and custom display names. Reduces test duplication by running the same test logic with multiple input values.

When to Use

• Writing JUnit tests with multiple input combinations

• Implementing data-driven tests in Java

• Running same test with different values (boundary analysis)

• Testing multiple scenarios from single test method

Instructions

• Add dependency: Ensure junit-jupiter-params is on test classpath (included in junit-jupiter )

• Choose source: @ValueSource for simple values, @CsvSource for tabular data, @MethodSource for complex objects

• Match parameters: Test method parameters must match data source types

• Set display names: Use name = "{0}..." for readable output

• Validate: Run ./gradlew test --info or mvn test and verify all parameter combinations execute

Examples

Maven / Gradle Dependency

JUnit 5 parameterized tests require junit-jupiter (includes params). Add assertj-core for assertions:

<!-- Maven --> <dependency> <groupId>org.junit.jupiter</groupId> <artifactId>junit-jupiter</artifactId> <scope>test</scope> </dependency>

// Gradle testImplementation("org.junit.jupiter:junit-jupiter")

@ValueSource — Simple Values

import org.junit.jupiter.params.ParameterizedTest; import org.junit.jupiter.params.provider.ValueSource; import static org.assertj.core.api.Assertions.*;

@ParameterizedTest @ValueSource(strings = {"hello", "world", "test"}) void shouldCapitalizeAllStrings(String input) { assertThat(StringUtils.capitalize(input)).isNotEmpty(); }

@ParameterizedTest @ValueSource(ints = {1, 2, 3, 4, 5}) void shouldBePositive(int number) { assertThat(number).isPositive(); }

@ParameterizedTest @ValueSource(ints = {Integer.MIN_VALUE, -1, 0, 1, Integer.MAX_VALUE}) void shouldHandleBoundaryValues(int value) { assertThat(Math.incrementExact(value)).isGreaterThan(value); }

@CsvSource — Tabular Data

import org.junit.jupiter.params.ParameterizedTest; import org.junit.jupiter.params.provider.CsvSource;

@ParameterizedTest @CsvSource({ "alice@example.com, true", "bob@gmail.com, true", "invalid-email, false", "user@, false", "@example.com, false" }) void shouldValidateEmailAddresses(String email, boolean expected) { assertThat(UserValidator.isValidEmail(email)).isEqualTo(expected); }

@MethodSource — Complex Data

import org.junit.jupiter.params.ParameterizedTest; import org.junit.jupiter.params.provider.MethodSource; import java.util.stream.Stream;

@ParameterizedTest @MethodSource("additionTestCases") void shouldAddNumbersCorrectly(int a, int b, int expected) { assertThat(Calculator.add(a, b)).isEqualTo(expected); }

static Stream<Arguments> additionTestCases() { return Stream.of( Arguments.of(1, 2, 3), Arguments.of(0, 0, 0), Arguments.of(-1, 1, 0), Arguments.of(100, 200, 300) ); }

@EnumSource — Enum Values

@ParameterizedTest @EnumSource(Status.class) void shouldHandleAllStatuses(Status status) { assertThat(status).isNotNull(); }

@ParameterizedTest @EnumSource(value = Status.class, names = {"ACTIVE", "INACTIVE"}) void shouldHandleSpecificStatuses(Status status) { assertThat(status).isIn(Status.ACTIVE, Status.INACTIVE); }

Custom Display Names

@ParameterizedTest(name = "Discount of {0}% should be calculated correctly") @ValueSource(ints = {5, 10, 15, 20}) void shouldApplyDiscount(int discountPercent) { double result = DiscountCalculator.apply(100.0, discountPercent); assertThat(result).isEqualTo(100.0 * (1 - discountPercent / 100.0)); }

Custom ArgumentsProvider

class RangeValidatorProvider implements ArgumentsProvider { @Override public Stream<? extends Arguments> provideArguments(ExtensionContext context) { return Stream.of( Arguments.of(0, 0, 100, true), Arguments.of(50, 0, 100, true), Arguments.of(-1, 0, 100, false), Arguments.of(101, 0, 100, false) ); } }

@ParameterizedTest @ArgumentsSource(RangeValidatorProvider.class) void shouldValidateRange(int value, int min, int max, boolean expected) { assertThat(RangeValidator.isInRange(value, min, max)).isEqualTo(expected); }

Error Condition Testing

@ParameterizedTest @ValueSource(strings = {"", " ", null}) void shouldThrowExceptionForInvalidInput(String input) { assertThatThrownBy(() -> Parser.parse(input)) .isInstanceOf(IllegalArgumentException.class); }

Best Practices

• Use descriptive display names: name = "{0}..." for readable output

• Test boundary values: include min, max, zero, and edge cases

• Keep test logic focused: single assertion per parameter set

• Use @MethodSource for complex objects, @CsvSource for tabular data

• Organize test data logically — group related scenarios together

Constraints and Warnings

• Parameter count must match: Number of parameters from source must match test method signature

• @ValueSource limitation: Only supports primitives, strings, and enums — not objects or null directly

• CSV escaping: Strings with commas must use single quotes in @CsvSource

• @MethodSource visibility: Factory methods must be static in the same test class

• Display name placeholders: Use {0} , {1} , etc. to reference parameters

• Execution count: Each parameter set runs as a separate test invocation

References

• JUnit 5 Parameterized Tests

• @ParameterizedTest API