BAEL-2305 Adds array intersection operations

core-java-arrays/src/test/java/com/baeldung/array/operations/IntersectionUnitTest.java

@@ -0,0 +1,66 @@
+package com.baeldung.array.operations;
+
+import org.junit.jupiter.api.Test;
+
+import static com.baeldung.array.operations.ArrayOperations.intersectionMultiSet;
+import static com.baeldung.array.operations.ArrayOperations.intersectionSet;
+import static com.baeldung.array.operations.ArrayOperations.intersectionSimple;
+import static org.assertj.core.api.Assertions.assertThat;
+
+class IntersectionUnitTest {
+    private static final Integer[] a = { 1, 3, 2 };
+    private static final Integer[] b = { 4, 3, 2, 4, 2, 3, 4, 4, 3 };
+    private static final Integer[] c = { 1, 3, 2, 3, 3, 2 };
+
+    @Test
+    void whenIntersectionSimpleIsUsed_thenCommonEntriesAreInTheResult() {
+        assertThat(intersectionSimple(a, b)).isEqualTo(new Integer[] { 3, 2 });
+        assertThat(intersectionSimple(b, a)).isEqualTo(new Integer[] { 3, 2, 2, 3, 3 });
+    }
+
+    @Test
+    void whenIntersectionSimpleIsUsedWithAnArrayAndItself_thenTheResultIsTheIdentity() {
+        assertThat(intersectionSimple(b, b)).isEqualTo(b);
+        assertThat(intersectionSimple(a, a)).isEqualTo(a);
+    }
+
+    @Test
+    void whenIntersectionSetIsUsed_thenCommonEntriesAreInTheResult() {
+        assertThat(intersectionSet(b, a)).isEqualTo(new Integer[] { 3, 2 });
+    }
+
+    @Test
+    void whenIntersectionSetIsUsed_thenTheNumberOfEntriesDoesNotChangeWithTheParameterOrder() {
+        assertThat(intersectionSet(a, b)).isEqualTo(new Integer[] { 3, 2 });
+        assertThat(intersectionSet(b, a)).isEqualTo(new Integer[] { 3, 2 });
+    }
+
+    @Test
+    void whenIntersectionSetIsUsedWithAnArrayAndWithItself_andTheInputHasNoDuplicateEntries_ThenTheResultIsTheIdentity() {
+        assertThat(intersectionSet(a, a)).isEqualTo(a);
+    }
+
+    @Test
+    void whenIntersectionSetIsUsedWithAnArrayAndWithItself_andTheInputHasDuplicateEntries_ThenTheResultIsNotTheIdentity() {
+        assertThat(intersectionSet(b, b)).isNotEqualTo(b);
+    }
+
+    @Test
+    void whenMultiSetIsUsed_thenCommonEntriesAreInTheResult() {
+        assertThat(intersectionMultiSet(b, a)).isEqualTo(new Integer[] { 3, 2 });
+    }
+
+    @Test
+    void whenIntersectionMultiSetIsUsed_thenTheNumberOfEntriesDoesNotChangeWithTheParameterOrder() {
+        assertThat(intersectionMultiSet(a, b)).isEqualTo(new Integer[] { 3, 2 });
+        assertThat(intersectionMultiSet(b, a)).isEqualTo(new Integer[] { 3, 2 });
+        assertThat(intersectionMultiSet(b, c)).isEqualTo(new Integer[] { 3, 2, 2, 3, 3 });
+        assertThat(intersectionMultiSet(c, b)).isEqualTo(new Integer[] { 3, 2, 3, 3, 2 });
+    }
+
+    @Test
+    void whenIntersectionMultiSetIsUsedWithAnArrayAndWithItself_ThenTheResultIsTheIdentity() {
+        assertThat(intersectionMultiSet(b, b)).isEqualTo(b);
+        assertThat(intersectionMultiSet(a, a)).isEqualTo(a);
+    }
+}