Unit Test Parameterized

# 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

1. **Add dependency**: Ensure `junit-jupiter-params` is on test classpath (included in `junit-jupiter`)
2. **Choose source**: `@ValueSource` for simple values, `@CsvSource` for tabular data, `@MethodSource` for complex objects
3. **Match parameters**: Test method parameters must match data source types
4. **Set display names**: Use `name = "{0}..."` for readable output
5. **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:

```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
@P