BAEL-2230 Equivalent of Java static final in Kotlin (#5848)

* constant unit test

* kotlin const

core-kotlin/src/test/kotlin/com/baeldung/kotlin/constant/ConstantUnitTest.kt

@@ -0,0 +1,17 @@
+import com.baeldung.kotlin.constant.TestKotlinConstantClass
+import com.baeldung.kotlin.constant.TestKotlinConstantObject
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+class ConstantUnitTest {
+
+    @Test
+    fun givenConstant_whenCompareWithActualValue_thenReturnTrue() {
+        assertEquals(10, TestKotlinConstantObject.COMPILE_TIME_CONST)
+        assertEquals(30, TestKotlinConstantObject.RUN_TIME_CONST)
+        assertEquals(20, TestKotlinConstantObject.JAVA_STATIC_FINAL_FIELD)
+
+        assertEquals(40, TestKotlinConstantClass.COMPANION_OBJECT_NUMBER)
+    }
+}
+

core-kotlin/src/test/kotlin/com/baeldung/kotlin/constant/TestKotlinConstantClass.kt

@@ -0,0 +1,8 @@
+package com.baeldung.kotlin.constant
+
+
+class TestKotlinConstantClass {
+    companion object {
+        const val COMPANION_OBJECT_NUMBER = 40
+    }
+}

core-kotlin/src/test/kotlin/com/baeldung/kotlin/constant/TestKotlinConstantObject.kt

@@ -0,0 +1,15 @@
+package com.baeldung.kotlin.constant
+
+
+object TestKotlinConstantObject {
+    const val COMPILE_TIME_CONST = 10
+
+    val RUN_TIME_CONST: Int
+
+    @JvmField
+    val JAVA_STATIC_FINAL_FIELD = 20
+
+    init {
+        RUN_TIME_CONST = TestKotlinConstantObject.COMPILE_TIME_CONST + 20;
+    }
+}