JUnit Input Space Partitioning

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.Arguments;
import org.junit.jupiter.params.provider.MethodSource;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Stream;

import static org.junit.jupiter.api.Assertions.*;

class SKITH1Test {

    // Interface-based tests
    @ParameterizedTest
    @MethodSource("generateTest1Data")
    void test1(List<String> list1, List<String> list2) {
        List<String> result = SKITH1.commonElements(list1, list2);
        assertTrue(result == null || result.size() > 0);
    }

    @ParameterizedTest
    @MethodSource("generateTest2Data")
    void test2(List<String> list1, List<String> list2) {
        assertNull(SKITH1.commonElements(list1, list2));
    }

    @ParameterizedTest
    @MethodSource("generateTest3Data")
    void test3(List<String> list1, List<String> list2) {
        assertThrows(NullPointerException.class, () -> SKITH1.commonElements(list1, list2));
    }

    @ParameterizedTest
    @MethodSource("generateTest4Data")
    void test4(List<String> list1, List<String> list2) {
        List<String> result = SKITH1.commonElements(list1, list2);
        assertTrue(result == null || result.size() > 0);
    }

    @ParameterizedTest
    @MethodSource("generateTest5Data")
    void test5(List<String> list1, List<String> list2) {
        assertThrows(NullPointerException.class, () -> SKITH1.commonElements(list1, list2));
    }


    static Stream<Arguments> generateTest1Data() {
        return Stream.of(
                Arguments.of(Arrays.asList("a", "b", "c"), Arrays.asList("d", "e", "f")),
                Arguments.of(Arrays.asList("g", "h", "i"), Arrays.asList("j", "k", "l"))
        );
    }

    static Stream<Arguments> generateTest2Data() {
        return Stream.of(
                Arguments.of(Arrays.asList("a", "b", "c"), List.of()),
                Arguments.of(Arrays.asList("a", "b", "c"), List.of()),
                Arguments.of(Arrays.asList("a", "b", "c"), List.of())
        );
    }

    static Stream<Arguments> generateTest3Data() {
        return Stream.of(
                Arguments.of(Arrays.asList("a", "b", "c"), null),
                Arguments.of(Arrays.asList("a", "b", "c"), null),
                Arguments.of(Arrays.asList("a", "b", "c"), null)
        );
    }

    static Stream<Arguments> generateTest4Data() {
        return Stream.of(
                Arguments.of(List.of(), Arrays.asList("a", "b", "c")),
                Arguments.of(List.of(), Arrays.asList("a", "b", "c"))
        );
    }

    static Stream<Arguments> generateTest5Data() {
        return Stream.of(
                Arguments.of(null, Arrays.asList("a", "b", "c")),
                Arguments.of(null, Arrays.asList("a", "b", "c"))
        );
    }

    // Functionality-based tests
    @ParameterizedTest
    @MethodSource("generateTest6Data")
    void test6(List<String> list1, List<String> list2) {
        List<String> result = SKITH1.commonElements(list1, list2);
        assertTrue(result.size() > 1);
    }

    @ParameterizedTest
    @MethodSource("generateTest7Data")
    void test7(List<String> list1, List<String> list2) {
        List<String> result = SKITH1.commonElements(list1, list2);
        assertTrue(result.size() == 1);
    }

    @ParameterizedTest
    @MethodSource("generateTest8Data")
    void test8(List<String> list1, List<String> list2) {
        assertNull(SKITH1.commonElements(list1, list2));
    }


    static Stream<Arguments> generateTest6Data() {
        return Stream.of(
                Arguments.of(Arrays.asList("a", "b", "c"), Arrays.asList("a", "b", "c")),
                Arguments.of(Arrays.asList("a", "b", "c"), Arrays.asList("a", "b", "c"))
        );
    }

    static Stream<Arguments> generateTest7Data() {
        return Stream.of(
                Arguments.of(Arrays.asList("a", "b", "c"), Arrays.asList("a", "d", "f")),
                Arguments.of(Arrays.asList("a", "b", "c"), Arrays.asList("a", "d", "f"))
        );
    }

    static Stream<Arguments> generateTest8Data() {
        return Stream.of(
                Arguments.of(Arrays.asList("a", "b", "c"), Arrays.asList("z", "d", "f")),
                Arguments.of(Arrays.asList("a", "b", "c"), Arrays.asList("z", "d", "f"))
        );
    }
}