Bael 2145 concatenate strings in kotlin (#5208)

* BAEL-2145

* BAEL-2145

* BAEL-2145

core-kotlin/src/test/kotlin/com/baeldung/kotlin/StringConcatenationTest.kt

@@ -0,0 +1,48 @@
+package com.baeldung.kotlin
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class StringConcatenationTest {
+
+    @Test
+    fun givenTwoStrings_concatenateWithTemplates_thenEquals() {
+        val a = "Hello"
+        val b = "Baeldung"
+        val c = "$a $b"
+
+        assertEquals("Hello Baeldung", c)
+    }
+
+    @Test
+    fun givenTwoStrings_concatenateWithPlusOperator_thenEquals() {
+        val a = "Hello"
+        val b = "Baeldung"
+        val c = a + " " + b
+
+        assertEquals("Hello Baeldung", c)
+    }
+
+    @Test
+    fun givenTwoStrings_concatenateWithStringBuilder_thenEquals() {
+        val a = "Hello"
+        val b = "Baeldung"
+
+        val builder = StringBuilder()
+        builder.append(a).append(" ").append(b)
+
+        val c = builder.toString()
+
+        assertEquals("Hello Baeldung", c)
+    }
+
+    @Test
+    fun givenTwoStrings_concatenateWithPlusMethod_thenEquals() {
+        val a = "Hello"
+        val b = "Baeldung"
+        val c = a.plus(" ").plus(b)
+
+        assertEquals("Hello Baeldung", c)
+    }
+
+}