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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-paramsis on test classpath (included injunit-jupiter) - Choose source:
@ValueSourcefor simple values,@CsvSourcefor tabular data,@MethodSourcefor 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 --infoormvn testand verify all parameter combinations execute
Examples
Maven / Gradle Dependency
JUnit 5 parameterized tests require junit-jupiter (includes params). Add assertj-core for assertions:
xml
<!-- Maven -->
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter</artifactId>
<scope>test</scope>
</dependency>kotlin
// Gradle
testImplementation("org.junit.jupiter:junit-jupiter")@ValueSource — Simple Values
java
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
java
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
java
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
java
@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
java
@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
java
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
java
@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
@MethodSourcefor complex objects,@CsvSourcefor 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
