Added a few unit tests for kotlin operator examples.

core-kotlin/src/test/kotlin/com/baeldung/operators/UtilsTest.kt

@@ -0,0 +1,13 @@
+package com.baeldung.operators
+
+import java.math.BigInteger
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class UtilsTest {
+
+    @Test
+    fun `We should be able to add an int value to an existing BigInteger using +`() {
+        assertEquals(BigInteger.ZERO + 1, BigInteger.ONE)
+    }
+}