Check if a year/date is a leap year in Java (#6086)

* Hexagonal architecture implementation in Java -
upendra.chintala@gmail.com

* An example program to find a leap year using java 8 java.time.Year API

* Changed to add assertions

* Remvoed evaluation article code

* Added unit test suite for leap year testing using java.time.Year and
java.util.GregorianCalendar

* Update LeapYearUnitTest.java

* Update LeapYearUnitTest.java

core-java/src/test/java/com/baeldung/leapyear/LeapYearUnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.leapyear;
+
+import java.time.Year;
+import java.util.GregorianCalendar;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class LeapYearUnitTest {
+	
+	//Before Java8
+	@Test
+	public void testLeapYearUsingGregorianCalendar () {
+		Assert.assertFalse(new GregorianCalendar().isLeapYear(2018));
+	}
+	
+	//Java 8 and above
+	@Test
+	public void testLeapYearUsingJavaTimeYear () {
+		Assert.assertTrue(Year.isLeap(2012));
+	}
+	
+	@Test
+	public void testBCYearUsingJavaTimeYear () {
+		Assert.assertTrue(Year.isLeap(-4));
+	}
+	
+	@Test
+	public void testWrongLeapYearUsingJavaTimeYear () {
+		Assert.assertFalse(Year.isLeap(2018));
+	}
+	
+	@Test
+	public void testLeapYearInDateUsingJavaTimeYear () {
+		LocalDate date = LocalDate.parse("2020-01-05", DateTimeFormatter.ISO_LOCAL_DATE);
+		Assert.assertTrue(Year.from(date).isLeap());
+	}
+	
+}