如何将相同的单元测试应用于不同的功能

Question

I am writing a class called Fibonacci which contains three static methods implementing three different implementations of the Fibonacci series using different approaches (recursion, memoization, etc.).

Then I've created a test package and inside it a simple junit test which checks whether an exception is thrown when a negative number is passed to the fibonacci function:

    @Test
void testIllegalArgumentException() {
    Assertions.assertThrows(IllegalArgumentException.class,
            () -> Fibonacci.fibonacci_recursive(-2));
}

My question is: is it possible to write one single test which takes a function as parameter? In other words I would like to avoid writing the following:

@Test
void testIllegalArgumentException() {
    Assertions.assertThrows(IllegalArgumentException.class,
            () -> Fibonacci.fibonacci_recursive(-2));
}
@Test
void testIllegalArgumentException() {
    Assertions.assertThrows(IllegalArgumentException.class,
            () -> Fibonacci.fibonacci_second(-2));
}
@Test
void testIllegalArgumentException() {
    Assertions.assertThrows(IllegalArgumentException.class,
            () -> Fibonacci.fibonacci_third(-2));
}

Answer 1

Java 8 + Junit5 allows you to create @ParameterizedTest . As list of parameters you can pass functions you want to test. Following test will run 3 times with different input functions.

Test sample:

    @ParameterizedTest
    @MethodSource("getSource")
    void whenNegativeValue_thenThrowException(Function<Integer, Integer> function, Integer value) {
        Assertions.assertThrows(IllegalArgumentException.class,
                () -> function.apply(value));
    }

    private static Stream<Arguments> getSource() {
        Function<Integer, Integer> first = Fib::first;
        Function<Integer, Integer> second = Fib::second;
        Function<Integer, Integer> third = Fib::third;
        return Stream.of(
                Arguments.of(first, -1),
                Arguments.of(second, -2),
                Arguments.of(third, -3)
        );
    }

Class implementation:

public class Fib {

    public static int first(int i) {
        System.out.println("first");
        validate(i);
        return i;
    }

    public static int second(int i) {
        System.out.println("second");
        validate(i);
        return i;
    }

    public static int third(int i) {
        System.out.println("third");
        validate(i);
        return i;
    }

    private static void validate(int i) {
        if (i < 0) {
            throw new IllegalArgumentException();
        }
    }

}

Answer 2

A basic approach would be to move the common code out to a helper that accepts the function to invoke and simply call that from the test(s).

// Helper
public void testFibo(Supplier<Integer> supplier) {
    Assertions.assertThrows(IllegalArgumentException.class,
        supplier.get());
}

// Usage inside test
testFibo(() -> Fibonacci.fibonacci_recursive(-2));

That said, testing frameworks can provide more elegant ways to this; I'm just not sure junit is one of them.