[JAVA-6143] java copy from one hashmap to another (#13497)

Co-authored-by: Bhaskar <bhaskar.dastidar@freshworks.com>

core-java-modules/core-java-collections-maps-6/src/test/java/com/baeldung/map/hashmapcopy/CopyHashMapIntoAnotherUnitTest.java

@@ -0,0 +1,68 @@
+package com.baeldung.map.hashmapcopy;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.baeldung.map.hashmapcopy.CopyingAHashMapToAnother;
+
+public class CopyHashMapIntoAnotherUnitTest {
+    @Test
+    public void givenSourceAndTargetMapsWhenIteratedOverThenCopyingSuccess(){
+        CopyingAHashMapToAnother obj = new CopyingAHashMapToAnother();
+        Assert.assertEquals(generateExpectedResultMap(), obj.copyByIteration(generateSourceMap(), generateTargetMap()));
+    }
+
+    @Test
+    public void givenSourceAndTargetMapsWhenUsedPutAllThenCopyingSuccess(){
+        CopyingAHashMapToAnother obj = new CopyingAHashMapToAnother();
+        Assert.assertEquals(generateExpectedResultMap(), obj.copyUsingPutAll(generateSourceMap(), generateTargetMap()));
+    }
+
+    @Test
+    public void givenSourceAndTargetMapsWhenUsedPutIfAbsentThenCopyingSuccess(){
+        CopyingAHashMapToAnother obj = new CopyingAHashMapToAnother();
+        Assert.assertEquals(generateExpectedResultMap(), obj.copyUsingPutIfAbsent(generateSourceMap(), generateTargetMap()));
+        Assert.assertEquals(generateExpectedResultMap(), obj.copyUsingPutIfAbsentForEach(generateSourceMap(), generateTargetMap()));
+    }
+
+    @Test
+    public void givenSourceAndTargetMapsWhenUsedMapMergeThenCopyingSuccess(){
+        CopyingAHashMapToAnother obj = new CopyingAHashMapToAnother();
+        Assert.assertEquals(generateExpectedResultMap(), obj.copyUsingMapMerge(generateSourceMap(), generateTargetMap()));
+    }
+
+    @Test
+    public void givenSourceAndTargetMapsWhenMapDifferenceUsedThenCopyingSuccess(){
+        CopyingAHashMapToAnother obj = new CopyingAHashMapToAnother();
+        Assert.assertEquals(generateExpectedResultMap(), obj.copyUsingGuavaMapDifference(generateSourceMap(), generateTargetMap()));
+    }
+
+    private Map<String, String> generateSourceMap(){
+        Map<String, String> sourceMap = new HashMap<>();
+        sourceMap.put("India", "Delhi");
+        sourceMap.put("United States", "Washington D.C.");
+        sourceMap.put("United Kingdom", "London DC");
+        return sourceMap;
+    }
+
+    private Map<String, String> generateTargetMap(){
+        Map<String, String> targetMap = new HashMap<>();
+        targetMap.put("Zimbabwe", "Harare");
+        targetMap.put("Norway", "Oslo");
+        targetMap.put("United Kingdom", "London");
+        return targetMap;
+    }
+
+    private Map<String, String> generateExpectedResultMap(){
+        Map<String, String> resultMap = new HashMap<>();
+        resultMap.put("India", "Delhi");
+        resultMap.put("United States", "Washington D.C.");
+        resultMap.put("United Kingdom", "London");
+        resultMap.put("Zimbabwe", "Harare");
+        resultMap.put("Norway", "Oslo");
+        return resultMap;
+    }
+}