JUnit 5: How to write test cases in enum

JUnit 5 provides ** @ParameterizedTest ** annotations that allow you to pass values from various argument sources to test methods as arguments. In this article, I would like to show you how to easily write many test cases by using one of these argument sources, ** @EnumSource **.

Preparation

If you use ** @ParameterizedTest **, you need to explicitly add junit-jupiter-params in addition to junit-jupiter-engine as project dependencies. Also, in this sample code, AssertJ was used to verify the test results.

pom.xml

<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-engine</artifactId>
    <version>5.5.1</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-params</artifactId>
    <version>5.5.1</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.assertj</groupId>
    <artifactId>assertj-core</artifactId>
    <version>3.13.1</version>
    <scope>test</scope>
</dependency>

Subject to test

Here, we will test the JDK's BigInteger # gcd () method. This method returns the greatest common divisor of itself and the given arguments.

Write a test case

Let's just describe the combination of two input values and the correct answer as an enum type constant.

enum GcdTestCase {
    THIS_IS_BIGGER(25, 10, 5),
    OTHER_IS_BIGGER(14, 21, 7),
    BOTH_ARE_EVEN(12, 8, 4),
    BOTH_ARE_ODD(27, 45, 9),
    BOTH_ARE_ZERO(0, 0, 0),
    BOTH_ARE_ONE(1, 1, 1),
    THIS_IS_ZERO(0, 3, 3),
    OTHER_IS_ZERO(4, 0, 4),
    THIS_IS_DIVISOR(3, 12, 3),
    OTHER_IS_DIVISOR(20, 4, 4),
    NO_COMMON_DIVISOR(7, 9, 1);

    final BigInteger a;
    final BigInteger b;
    final BigInteger expected;

    GcdTestCase(long a, long b, long expected) {
        this.a = BigInteger.valueOf(a);
        this.b = BigInteger.valueOf(b);
        this.expected = BigInteger.valueOf(expected);
    }
}

I created 11 test cases for the time being, but it's relatively easy to add test cases later. Just increase the enumerator.

Write a test method

Specify the ** @ParameterizedTest ** annotation for the test method, and at the same time specify the enum type created above using the ** @EnumSource ** annotation.

@ParameterizedTest
@EnumSource(GcdTestCase.class)
public void gcdShouldReturnGreatestCommonDivisorAsExpected(GcdTestCase test) {
    BigInteger actual = test.a.gcd(test.b);
    assertThat(actual).isEqualTo(test.expected);
}

Run the test

If you run the test you created with mvn test, of course, all the tests will succeed.

[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running org.example.junit5.tips.BigIntegerTest
[INFO] Tests run: 11, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.156 s - in org.example.junit5.tips.BigIntegerTest
[INFO]
[INFO] Results:
[INFO]
[INFO] Tests run: 11, Failures: 0, Errors: 0, Skipped: 0

Summary

This time, I introduced how to easily write many test cases using ** @EnumSource ** of JUnit 5. The sample code is posted on GitHub. The license is The Unlicense.