BAEL-2403: Immutable Map implementations in Java (eugenp#5828)

* BAEL-2203 - Convert java.time.Instant to java.sql.Timestamp and vice-versa

* BAEL-2203: Review edits

* Removed ZoneId code

* Converted class to JUnit Test

* Update and rename ConvertInstantToTimestampTest.java to ConvertInstantToTimestampUnitTest.java

* BAEL-2403: Immutable Map implementations in Java

* BAEL-2403: Immutable Map implementations in Java - Changed file name

Author: horizonfrost

java-collections-maps/src/test/java/com/baeldung/java/map/ImmutableMapUnitTest.java

@@ -0,0 +1,87 @@
+package com.baeldung.java.map;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+import com.google.common.collect.ImmutableMap;
+
+
+public class ImmutableMapUnitTest {
+
+	@Test
+	public void whenCollectionsUnModifiableMapMethod_thenOriginalCollectionChangesReflectInUnmodifiableMap() {
+
+		Map<String, String> mutableMap = new HashMap<>();
+		mutableMap.put("USA", "North America");
+
+		Map<String, String> unmodifiableMap = Collections.unmodifiableMap(mutableMap);
+		assertThrows(UnsupportedOperationException.class, () -> unmodifiableMap.put("Canada", "North America"));
+		
+		mutableMap.remove("USA");
+		assertFalse(unmodifiableMap.containsKey("USA"));
+		
+		mutableMap.put("Mexico", "North America");
+		assertTrue(unmodifiableMap.containsKey("Mexico"));
+	}
+	
+	@Test
+	@SuppressWarnings("deprecation")
+	public void whenGuavaImmutableMapFromCopyOfMethod_thenOriginalCollectionChangesDoNotReflectInImmutableMap() {
+
+		Map<String, String> mutableMap = new HashMap<>();
+		mutableMap.put("USA", "North America");
+
+		ImmutableMap<String, String> immutableMap = ImmutableMap.copyOf(mutableMap);
+		assertTrue(immutableMap.containsKey("USA"));
+		
+		assertThrows(UnsupportedOperationException.class, () -> immutableMap.put("Canada", "North America"));
+		
+		mutableMap.remove("USA");
+		assertTrue(immutableMap.containsKey("USA"));
+		
+		mutableMap.put("Mexico", "North America");
+		assertFalse(immutableMap.containsKey("Mexico"));
+	}
+	
+	@Test
+	@SuppressWarnings("deprecation")
+	public void whenGuavaImmutableMapFromBuilderMethod_thenOriginalCollectionChangesDoNotReflectInImmutableMap() {
+
+		Map<String, String> mutableMap = new HashMap<>();
+		mutableMap.put("USA", "North America");
+
+		ImmutableMap<String, String> immutableMap = ImmutableMap.<String, String>builder()
+				.putAll(mutableMap)
+				.put("Costa Rica", "North America")
+				.build();
+		assertTrue(immutableMap.containsKey("USA"));
+		assertTrue(immutableMap.containsKey("Costa Rica"));
+		
+		assertThrows(UnsupportedOperationException.class, () -> immutableMap.put("Canada", "North America"));
+		
+		mutableMap.remove("USA");
+		assertTrue(immutableMap.containsKey("USA"));
+		
+		mutableMap.put("Mexico", "North America");
+		assertFalse(immutableMap.containsKey("Mexico"));
+	}
+	
+	@Test
+	@SuppressWarnings("deprecation")
+	public void whenGuavaImmutableMapFromOfMethod_thenOriginalCollectionChangesDoNotReflectInImmutableMap() {
+
+		ImmutableMap<String, String> immutableMap = ImmutableMap.of("USA", "North America", "Costa Rica", "North America");
+		assertTrue(immutableMap.containsKey("USA"));
+		assertTrue(immutableMap.containsKey("Costa Rica"));
+
+		assertThrows(UnsupportedOperationException.class, () -> immutableMap.put("Canada", "North America"));
+	}
+	
+}