added test case demonstrating equality/hashCode issues with Collections.unmodifiableCollection

java/com.sap.sailing.domain.test/src/com/sap/sailing/domain/test/UnmodifiableCollectionsEqualsHashCodeTest.java

@@ -0,0 +1,58 @@
+package com.sap.sailing.domain.test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import org.junit.Test;
+
+/**
+ * Demonstrates how unmodifiable collections' hashCode and equals is useless because it's based on identity and not on
+ * content.
+ * 
+ * @author Axel Uhl (D043530)
+ *
+ */
+public class UnmodifiableCollectionsEqualsHashCodeTest {
+    @Test
+    public void testInequalityOfUnmodifiableCollection() {
+        List<String> l1 = Arrays.asList(new String[] { "abc", "def" });
+        List<String> l2 = new ArrayList<>(l1);
+        Iterable<String> u1_1 = Collections.unmodifiableCollection(l1);
+        Iterable<String> u1_2 = Collections.unmodifiableCollection(l1);
+        Iterable<String> u2_1 = Collections.unmodifiableCollection(l2);
+        assertEquals(l1, l2);
+        assertFalse(u1_1.equals(u1_2));
+        assertFalse(u1_1.equals(u2_1));
+    }
+
+    @Test
+    public void testInequalityOfUnmodifiableList() {
+        List<String> l1 = Arrays.asList(new String[] { "abc", "def" });
+        List<String> l2 = new ArrayList<>(l1);
+        Iterable<String> u1_1 = Collections.unmodifiableList(l1);
+        Iterable<String> u1_2 = Collections.unmodifiableList(l1);
+        Iterable<String> u2_1 = Collections.unmodifiableList(l2);
+        assertEquals(l1, l2);
+        assertEquals(u1_1, u1_2);
+        assertEquals(u1_1, u2_1);
+    }
+
+    @Test
+    public void testInequalityOfUnmodifiableSet() {
+        Set<String> s1 = new HashSet<>(Arrays.asList(new String[] { "abc", "def" }));
+        Set<String> s2 = new HashSet<>(s1);
+        Iterable<String> u1_1 = Collections.unmodifiableSet(s1);
+        Iterable<String> u1_2 = Collections.unmodifiableSet(s1);
+        Iterable<String> u2_1 = Collections.unmodifiableSet(s2);
+        assertEquals(s1, s2);
+        assertEquals(u1_1, u1_2);
+        assertEquals(u1_1, u2_1);
+    }
+}