KTLN-141: Not-Null Assertion (!!) Operator in Kotlin (#9371)

* Added the Test Samples

* Renamed the Class

core-kotlin-modules/core-kotlin-2/src/test/kotlin/com/baeldung/nullassertion/NotNullAssertionUnitTest.kt

@@ -0,0 +1,20 @@
+package com.baeldung.nullassertion
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class NotNullAssertionUnitTest {
+
+    @Test
+    fun givenNullableValue_WhenNotNull_ShouldExtractTheValue() {
+        val answer: String? = "42"
+
+        assertEquals(42, answer!!.toInt())
+    }
+
+    @Test(expected = KotlinNullPointerException::class)
+    fun givenNullableValue_WhenIsNull_ThenShouldThrow() {
+        val noAnswer: String? = null
+        noAnswer!!
+    }
+}