Add unit tests (#14306)

core-java-modules/core-java-8-datetime-2/src/test/java/com/baeldung/instantvslocaldatetime/InstantAndLocalDateTimeUnitTest.java

@@ -0,0 +1,41 @@
+package com.baeldung.instantvslocaldatetime;
+
+import org.junit.Test;
+
+import java.time.Instant;
+import java.time.LocalDateTime;
+import java.time.temporal.ChronoUnit;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class InstantAndLocalDateTimeUnitTest {
+
+    @Test
+    public void givenTwoInstants_whenComparing_thenDifferent() {
+
+        // Instant arithmetic
+        Instant.now().plus(12, ChronoUnit.HOURS);
+        Instant oneWeekAgo = Instant.now().minus(7, ChronoUnit.DAYS);
+
+        // Comparing 2 Instants
+        Instant instant1 = Instant.now();
+        Instant instant2 = instant1.plus(1, ChronoUnit.SECONDS);
+        assertTrue(instant1.isBefore(instant2));
+        assertFalse(instant1.isAfter(instant2));
+    }
+
+    @Test
+    public void givenTwoLocalDateTimes_whenComparing_thenDifferent() {
+
+        // LocalDateTime arithmetic
+        LocalDateTime tomorrow = LocalDateTime.now().plus(1, ChronoUnit.DAYS);
+        LocalDateTime oneYearAgo = LocalDateTime.now().minus(1, ChronoUnit.YEARS);
+
+        // Comparing 2 LocalDateTimes
+        LocalDateTime now = LocalDateTime.now();
+        LocalDateTime y2k = LocalDateTime.of(2000, 1, 1, 0, 0);
+        assertTrue(now.isAfter(y2k));
+        assertTrue(y2k.isBefore(now));
+    }
+}