[duration-improvement] isNegative, isZero Tests (#14791)

core-java-modules/core-java-8-datetime/src/test/java/com/baeldung/dateapi/JavaDurationUnitTest.java

@@ -3,9 +3,11 @@ package com.baeldung.dateapi;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.time.Duration;
 import java.time.Instant;
+import java.time.LocalDateTime;
 import java.time.LocalTime;
 import java.time.temporal.ChronoUnit;
 
@@ -34,6 +36,22 @@ public class JavaDurationUnitTest {
         assertThat(seconds).isEqualTo(30);
     }
 
+    @Test
+    public void givenADuration_whenCallingisZeroAndisNegative_thenGetExpectedResult() {
+        LocalDateTime start = LocalDateTime.parse("2020-01-01T08:00:00");
+        LocalDateTime end = LocalDateTime.parse("2020-01-01T12:00:00");
+        assertFalse(Duration.between(start, end)
+          .isNegative());
+        assertTrue(Duration.between(end, start)
+          .isNegative());
+
+        LocalDateTime theTime = LocalDateTime.parse("2023-09-09T08:00:00");
+        assertTrue(Duration.between(theTime, theTime)
+          .isZero());
+        assertFalse(Duration.between(theTime, theTime)
+          .isNegative());
+    }
+
     @Test
     public void test2() {
         Instant start = Instant.parse("2017-10-03T10:15:30.00Z");