ClassicalTDD.java

@Test
public void 2001_isCommon() {
    boolean result = isLeapYear(2001);

    assertThat(result).isFalse();
}

@Test
public void 1996_isLeap() {
    boolean result = isLeapYear(1996);

    assertThat(result).isTrue();
}

// more test cases until there are enough to triangulate all the possible scenarios

boolean isLeapYear(int year) {
    return ((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0);   
}