JUnit5 Jupiter (7) Test for Interface Contracts

JUnit5 Jupiter (7) Test for Interface Contracts, Object.equals, Comparable.compareTo

public interface Testable<T> {
    T createValue();}

public interface EqualsContract<T> extends Testable<T> {
    T createNotEqualValue();
    @Test 

    default void valueEqualsItself() {
        T value = createValue();    }

    @Test     

    default void valueDoesNotEqualsNull() {
      T value = createValue(); 

      assertFalse( value.equals(null));    }

    @Test 

    default void valueDoesNotEqualDifferentValue() {
        T value = createValue(); 

        T differentValue = createNotEqualValue(); 

        assertNotEquals( value, differentValue); 

        assertNotEquals( differentValue, value);    }
}

public interface ComparableContract<T extends Comparable<T>> extends Testable<T> {
    T createSmallerValue();
    @Test     

    default void returnsZeroWhenComparableWithItself() {
        T value = createValue(); 

        assertEquals( 0, value.compareTo( value)); 

    }

    @Test 

    default void returnsPositiveNumberWhenComparedToSmallerValue() {
        T value = createValue(); 

        T smallerValue = createSmallerValue(); 

        assertTrue( value.compareTo(smallerValue) > 0); 

    }

    @Test     

    default void returnsNegativeNumberWhenCompareToLargerValue() {
        T value = createValue(); 

        T smallerValue = createSmallerValue(); 

        assertTrue( smallerValue.compareTo( value) < 0);     

    }
}

public class StringTest implements ComparableContract<String>, EqualsContract<String> {
    @Override     

    public String createValue() {
        return "M_empiezaconM"; 

    }

    @Override     

    public String createSmallerValue() {
        return "B_masChicoQue_M";     

    }

    @Override     

    public String createNotEqualValue() {
        return "X_diferenteACreateValue";     

    }
}

Run Test

eot