step-by-step.md

Day 6: Parameterize your tests.

Parameterized tests can save us a lot of time. Know more about this concept in java here.

• We start by adding the dependency on junit-jupiter-params
  • Not really needed here because we already have the dependency junit-jupiter in our parent pom.xml file

<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-params</artifactId>
    <version>${junit.version}</version>
    <scope>test</scope>
</dependency>

• We adapt the first test
  • By extracting parameters

• Then, we define a method source

• We set the values for this test

public static Stream<Arguments> validInputs() {
    return Stream.of(
            Arguments.of(1, "1")
    );
}

• The test is green...

Don't Trust Tests. Unless you have seen they fail first.

• Let's make it fail for a good reason to be sure we can trust it
  • We change the expectedResult for that

• We are pretty confident, so let's move other tests in validInputs

public static Stream<Arguments> validInputs() {
    return Stream.of(
            Arguments.of(1, "1"),
            Arguments.of(67, "67"),
            Arguments.of(82, "82"),
            Arguments.of(3, "Fizz"),
            Arguments.of(66, "Fizz"),
            Arguments.of(99, "Fizz"),
            Arguments.of(5, "Buzz"),
            Arguments.of(50, "Buzz"),
            Arguments.of(85, "Buzz"),
            Arguments.of(15, "FizzBuzz"),
            Arguments.of(30, "FizzBuzz"),
            Arguments.of(45, "FizzBuzz")
    );
}

@ParameterizedTest
@MethodSource("validInputs")
void returns_number_representation(int input, String expectedResult) throws OutOfRangeException {
    assertThat(FizzBuzz.convert(input))
            .isEqualTo(expectedResult);
}

• With Parameterized Tests it could be tempting to write this kind of test
  • Here, add edge cases inside the test...

public static Stream<Arguments> validInputs() {
    return Stream.of(
            Arguments.of(1, "1"),
            Arguments.of(67, "67"),
            Arguments.of(82, "82"),
            Arguments.of(3, "Fizz"),
            Arguments.of(66, "Fizz"),
            Arguments.of(99, "Fizz"),
            Arguments.of(5, "Buzz"),
            Arguments.of(50, "Buzz"),
            Arguments.of(85, "Buzz"),
            Arguments.of(15, "FizzBuzz"),
            Arguments.of(30, "FizzBuzz"),
            Arguments.of(45, "FizzBuzz"),
            Arguments.of(0, null)
    );
}

@ParameterizedTest
@MethodSource("validInputs")
void returns_number_representation(int input, String expectedResult) throws OutOfRangeException {
    if (expectedResult != null) {
        assertThat(FizzBuzz.convert(input))
                .isEqualTo(expectedResult);
    } else {
        assertThatThrownBy(() -> FizzBuzz.convert(input))
                .isInstanceOf(OutOfRangeException.class);
    }
}

• One advice for you, try to avoid to take decisions in your tests
  • Decisions mean you have different test cases...
  • Have dedicated test methods for specific test cases

public static Stream<Arguments> validInputs() {
    return Stream.of(
            Arguments.of(1, "1"),
            Arguments.of(67, "67"),
            Arguments.of(82, "82"),
            Arguments.of(3, "Fizz"),
            Arguments.of(66, "Fizz"),
            Arguments.of(99, "Fizz"),
            Arguments.of(5, "Buzz"),
            Arguments.of(50, "Buzz"),
            Arguments.of(85, "Buzz"),
            Arguments.of(15, "FizzBuzz"),
            Arguments.of(30, "FizzBuzz"),
            Arguments.of(45, "FizzBuzz")
    );
}

public static Stream<Arguments> invalidInputs() {
    return Stream.of(
            Arguments.of(0),
            Arguments.of(-1),
            Arguments.of(101)
    );
}

@ParameterizedTest
@MethodSource("validInputs")
void returns_number_representation(int input, String expectedResult) throws OutOfRangeException {
    assertThat(FizzBuzz.convert(input))
            .isEqualTo(expectedResult);
}

@ParameterizedTest
@MethodSource("invalidInputs")
void throws_an_exception_for_numbers_out_of_range(int input) {
    assertThatThrownBy(() -> FizzBuzz.convert(input))
            .isInstanceOf(OutOfRangeException.class);
}