KTLN-478: Merging Two Maps in Kotlin

core-kotlin-modules/core-kotlin-collections-map/src/test/kotlin/com/baeldung/mergemap/MergeMapUnitTest.kt

@@ -0,0 +1,62 @@
+package com.baeldung.mergemap
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+class MergeMapUnitTest {
+
+    @Test
+    fun `Return new merged map after merging two maps with plus operator`() {
+        val map1 = mapOf("a" to 1, "b" to 2)
+        val map2 = mapOf("b" to 3, "c" to 4)
+
+        val mergedMap = map1 + map2
+
+        assertEquals(mapOf("a" to 1, "b" to 3, "c" to 4), mergedMap)
+    }
+
+    @Test
+    fun `First map contains result of merging with second map using the putAll method`() {
+        val map1 = mutableMapOf("a" to 1, "b" to 2)
+        val map2 = mapOf("b" to 3, "c" to 4)
+
+        map1.putAll(map2)
+
+        assertEquals(mapOf("a" to 1, "b" to 3, "c" to 4), map1)
+    }
+
+    @Test
+    fun `Return new merged map after merging two maps with plus assign operator`() {
+        val map1 = mutableMapOf("a" to 1, "b" to 2)
+        val map2 = mapOf("b" to 3, "c" to 4)
+
+        map1 += map2
+
+        assertEquals(mapOf("a" to 1, "b" to 3, "c" to 4), map1)
+    }
+
+    @Test
+    fun `Return new merged map after merging two maps using assicateWith function`() {
+        val map1 = mapOf("a" to 1, "b" to 2)
+        val map2 = mapOf("b" to 3, "c" to 4)
+
+        val mergedMap = (map1.keys + map2.keys).associateWith {
+          key -> map2[key] ?: map1[key]!!
+        }
+
+        assertEquals(mapOf("a" to 1, "b" to 3, "c" to 4), mergedMap)
+    }
+
+    @Test
+    fun `Second map contains result of merging two maps using Java Map merge function`() {
+        val map1 = mutableMapOf("a" to 1, "b" to 2)
+        val map2 = mapOf("b" to 3, "c" to 4)
+
+        map2.forEach { (key, value) ->
+            map1.merge(key, value) { oldVal, newVal -> newVal * oldVal }
+        }
+
+        assertEquals(mapOf("a" to 1, "b" to 6, "c" to 4), map1)
+    }
+
+}