GH-1225 Add additional Kotlin test to verify the regression

Resolves #1225

spring-cloud-function-kotlin/src/test/java/org/springframework/cloud/function/kotlin/ContextFunctionCatalogAutoConfigurationKotlinTests.java

@@ -32,6 +32,8 @@
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.core.ResolvableType;
+import org.springframework.messaging.Message;
 import org.springframework.messaging.support.MessageBuilder;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -57,7 +59,8 @@ public void typeDiscoveryTests() {
 		create(new Class[] { KotlinLambdasConfiguration.class,
 				SimpleConfiguration.class,
 				KotlinComponentFunction.class,
-				ComponentUppercase.class});
+				ComponentUppercase.class,
+				ComponentWithUnitReturn.class});
 
 		FunctionCatalog functionCatalog = this.context.getBean(FunctionCatalog.class);
 
@@ -72,6 +75,10 @@ public void typeDiscoveryTests() {
 		assertThat(kotlinFunction.getInputType()).isEqualTo(String.class);
 		assertThat(kotlinFunction.getOutputType()).isEqualTo(String.class);
 
+		FunctionInvocationWrapper componentWithUnitReturn = functionCatalog.lookup("componentWithUnitReturn");
+		assertThat(componentWithUnitReturn.isConsumer()).isTrue();
+		assertThat(componentWithUnitReturn.getInputType()).isEqualTo(ResolvableType.forClassWithGenerics(Message.class, String.class).getType());
+
 		FunctionInvocationWrapper kotlinConsumer = functionCatalog.lookup("kotlinConsumer");
 		assertThat(kotlinConsumer.isConsumer()).isTrue();
 		assertThat(kotlinConsumer.getInputType()).isEqualTo(String.class);

spring-cloud-function-kotlin/src/test/kotlin/org/springframework/cloud/function/kotlin/ComponentWithUnitReturn.kt

@@ -0,0 +1,11 @@
+package org.springframework.cloud.function.kotlin
+
+import org.springframework.messaging.Message
+import org.springframework.stereotype.Component
+
+@Component
+class ComponentWithUnitReturn() : (Message<String>) -> Unit {
+	override fun invoke(message: Message<String>) {
+		println(message.payload)
+	}
+}