Modulus of Negative Numbers in Java (#14640)

core-java-modules/core-java-lang-operators/src/test/java/com/baeldung/modulo/ModuloUnitTest.java

@@ -1,5 +1,7 @@
 package com.baeldung.modulo;
 
+import static org.junit.Assert.assertEquals;
+
 import org.junit.Test;
 import static org.assertj.core.api.Java6Assertions.*;
 
@@ -40,6 +42,27 @@ public class ModuloUnitTest {
         assertThat(4 % 2).isEqualTo(0);
     }
 
+    @Test
+    public void whenDividendIsNegativeAndModulusIs2_thenResultIsNegative() {
+        assertEquals(-1, -9 % 2);
+    }
+
+    @Test
+    public void whenDividendIsNegativeAndRemainderIsCheckedForNegativeValue_thenResultIsPositive() {
+        int remainder = -9 % 2;
+
+        if (remainder < 0) {
+            remainder += 2;
+        }
+        assertEquals(1, remainder);
+    }
+
+    @Test
+    public void whenDividendIsNegativeAndUsesMathClass_thenResultIsPositive() {
+        int remainder = Math.floorMod(-9, 2);
+        assertEquals(1, remainder);
+    }
+
     @Test
     public void whenItemsIsAddedToCircularQueue_thenNoArrayIndexOutOfBounds() {
         int QUEUE_CAPACITY = 10;