Make WebTestClientExtensions.expectBody generics compliant

Closes gh-24142

spring-test/src/main/kotlin/org/springframework/test/web/reactive/server/WebTestClientExtensions.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -68,7 +68,7 @@ inline fun <reified T : Any> RequestBodySpec.body(flow: Flow<T>): RequestHeaders
  */
 @Suppress("EXTENSION_SHADOWED_BY_MEMBER")
 inline fun <reified B : Any> ResponseSpec.expectBody(): KotlinBodySpec<B> =
-		expectBody(B::class.java).returnResult().let {
+		expectBody(object : ParameterizedTypeReference<B>() {}).returnResult().let {
 			object : KotlinBodySpec<B> {
 
 				override fun isEqualTo(expected: B): KotlinBodySpec<B> = it

spring-test/src/test/kotlin/org/springframework/test/web/reactive/server/WebTestClientExtensionsTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -62,7 +62,7 @@ class WebTestClientExtensionsTests {
 	@Test
 	fun `ResponseSpec#expectBody with reified type parameters`() {
 		responseSpec.expectBody<Foo>()
-		verify { responseSpec.expectBody(Foo::class.java) }
+		verify { responseSpec.expectBody(object : ParameterizedTypeReference<Foo>() {}) }
 	}
 
 	@Test