Add MetadataExtractorRegistry.metadataToExtract Kotlin extensions

Closes gh-23705

spring-messaging/src/test/kotlin/org/springframework/messaging/rsocket/MetadataExtractorRegistryExtensions.kt

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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.springframework.messaging.rsocket
+
+import io.mockk.mockk
+import io.mockk.verify
+import org.junit.jupiter.api.Test
+import org.springframework.core.ParameterizedTypeReference
+import org.springframework.util.MimeType
+import java.util.function.BiConsumer
+
+class MetadataExtractorRegistryExtensions {
+
+	@Test
+	fun `metadataToExtract with String parameter`() {
+		val extractor = mockk<MetadataExtractorRegistry>(relaxed = true)
+		val name = "name"
+		val mimeType = MimeType.valueOf("application/json")
+		extractor.metadataToExtract<String>(mimeType, name)
+		verify {
+			extractor.metadataToExtract(mimeType, object: ParameterizedTypeReference<String>() {}, name)
+		}
+	}
+
+	@Test
+	fun `metadataToExtract with BiConsumer parameter`() {
+		val extractor = mockk<MetadataExtractorRegistry>(relaxed = true)
+		val name = "name"
+		val mimeType = MimeType.valueOf("application/json")
+		extractor.metadataToExtract<Map<String, String>>(mimeType) { jsonMap, outputMap ->
+			outputMap.putAll(jsonMap)
+		}
+		verify {
+			extractor.metadataToExtract(mimeType, object: ParameterizedTypeReference<Map<String, String>>() {}, any<BiConsumer<Map<String, String>, MutableMap<String, Any>>>())
+		}
+	}
+}