test: add coverage on map helper

Author: fbiville

testing/src/main/kotlin/org/neo4j/connectors/kafka/testing/MapSupport.kt

@@ -23,7 +23,7 @@ internal object MapSupport {
   @Suppress("UNCHECKED_CAST")
   fun <K, Any> MutableMap<K, Any>.nestUnder(key: K, values: Map<K, Any>): MutableMap<K, Any> {
     val map = this[key]
-    if (map !is MutableMap<*, *>) {
+    if (map !is Map<*, *>) {
       throw IllegalStateException("entry at key $key is not a mutable map")
     }
     (map as MutableMap<K, Any>).putAll(values)

testing/src/test/kotlin/org/neo4j/connectors/kafka/testing/MapSupportTest.kt

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) "Neo4j"
+ * Neo4j Sweden AB [http://neo4j.com]
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.neo4j.connectors.kafka.testing
+
+import java.lang.IllegalStateException
+import org.junit.jupiter.api.Assertions.*
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
+import org.neo4j.connectors.kafka.testing.MapSupport.nestUnder
+
+class MapSupportTest {
+
+  @Test
+  fun `nests map under specified key`() {
+    val initialMap = mutableMapOf<String, Any>("foo" to mutableMapOf("bar" to "baz"))
+
+    val result = initialMap.nestUnder("foo", mapOf("fighters" to "rocks"))
+
+    assertEquals(mutableMapOf("foo" to mutableMapOf("bar" to "baz", "fighters" to "rocks")), result)
+  }
+
+  @Test
+  fun `fails to nest map if key's value is not a map`() {
+    val initialMap = mutableMapOf<String, Any>("foo" to "bar")
+
+    val exception =
+        assertThrows<IllegalStateException> {
+          initialMap.nestUnder("foo", mapOf("fighters" to "rocks"))
+        }
+    assertEquals(exception.message, "entry at key foo is not a mutable map")
+  }
+}