The same remarks apply as for “Refactoring the Traditional for Loop”

• No init()
• Classes under test implement a common interface that is called in tests.
• Negative tests which apply for input less than 1900, resulting in exceptions.

package chapter11; import org.junit.jupiter.api.Test; import java.time.Year; import java.util.stream.IntStream; import static org.junit.jupiter.api.Assertions.*; // Everything is inside the MoreComplexLoopTest class for convenience. // Documentation for java.time.Year.isLeap() // https://docs.oracle.com/javase/8/docs/api/java/time/Year.html#isLeap-- public class MoreComplexLoopTest { interface LeapYears { int countFrom1900(int upTo); } static class LeapYearCountBefore implements LeapYears { public int countFrom1900(int upTo) { if (upTo < 1900) { throw new IllegalArgumentException("The passed value is < 1900: " + upTo); } int count = 0; for (int year = 1900; year <= upTo; year += 4) { if (Year.isLeap(year)) { count++; } } return count; } } static class LeapYearCountAfter implements LeapYears { public int countFrom1900(int upTo) { if (upTo < 1900) { throw new IllegalArgumentException("The passed value is < 1900: " + upTo); } return (int) IntStream.iterate(1900, year -> year <= upTo, year -> year + 4) .filter(Year::isLeap) .count(); } } private static void commonLeapYearsTests(final LeapYears leapYears) { assertAll( () -> assertEquals(0, leapYears.countFrom1900(1900)), () -> assertEquals(25, leapYears.countFrom1900(2000)), () -> assertEquals(27, leapYears.countFrom1900(2010)), () -> assertEquals(31, leapYears.countFrom1900(2025)), () -> assertEquals(49, leapYears.countFrom1900(2100)), () -> assertEquals(267, leapYears.countFrom1900(3000)), () -> assertThrows(IllegalArgumentException.class, () -> leapYears.countFrom1900(1800)) ); } @Test void leapYearCountBefore() { commonLeapYearsTests(new LeapYearCountBefore()); } @Test void leapYearCountAfter() { commonLeapYearsTests(new LeapYearCountAfter()); } }