Add Kotlin extensions for RestTestClient

Closes gh-35558

spring-test/src/main/kotlin/org/springframework/test/web/servlet/client/RestTestClientExtensions.kt

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2002-present 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.test.web.servlet.client
+
+import org.springframework.core.ParameterizedTypeReference
+import org.springframework.test.web.servlet.client.RestTestClient.BodySpec
+import org.springframework.test.web.servlet.client.RestTestClient.ResponseSpec
+
+/**
+ * Extension for [ResponseSpec.expectBody] providing an `expectBody<Foo>()` variant
+ * leveraging Kotlin reified type parameters. This extension is not subject ot type
+ * erasure and retains actual generic type arguments.
+ *
+ * @author Sebastien Deleuze
+ * @author Arjen Poutsma
+ * @author Stephane Nicoll
+ * @since 7.0
+ */
+inline fun <reified B : Any> ResponseSpec.expectBody(): BodySpec<B, *> =
+		expectBody(object : ParameterizedTypeReference<B>() {})
+
+/**
+ * Extension for [ResponseSpec.returnResult] providing a `returnResult<Foo>()` variant.
+ *
+ * @author Sebastien Deleuze
+ * @since 7.0
+ */
+inline fun <reified T : Any> ResponseSpec.returnResult(): EntityExchangeResult<T> =
+		returnResult(object : ParameterizedTypeReference<T>() {})

spring-test/src/test/kotlin/org/springframework/test/web/servlet/client/RestTestClientExtensionsTests.kt

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2002-present 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.test.web.servlet.client
+
+import io.mockk.mockk
+import io.mockk.verify
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+import org.springframework.core.ParameterizedTypeReference
+import org.springframework.web.bind.annotation.GetMapping
+import org.springframework.web.bind.annotation.RestController
+
+/**
+ * Mock object based tests for [RestTestClient] Kotlin extensions
+ *
+ * @author Sebastien Deleuze
+ * @author Stephane Nicoll
+ */
+class RestTestClientExtensionsTests {
+
+	private val responseSpec = mockk<RestTestClient.ResponseSpec>(relaxed = true)
+
+
+	@Test
+	fun `ResponseSpec#expectBody with reified type parameters`() {
+		responseSpec.expectBody<Foo>()
+		verify { responseSpec.expectBody(object : ParameterizedTypeReference<Foo>() {}) }
+	}
+
+	@Test
+	fun `KotlinBodySpec#isEqualTo`() {
+		RestTestClient
+				.bindToController(TestController())
+				.build()
+				.get().uri("/").exchange().expectBody<String>().isEqualTo("foo")
+	}
+
+	@Test
+	fun `KotlinBodySpec#consumeWith`() {
+		RestTestClient
+				.bindToController(TestController())
+				.build()
+				.get().uri("/").exchange().expectBody<String>()
+				.consumeWith { assertThat(it.responseBody).isEqualTo("foo") }
+	}
+
+	@Test
+	fun `KotlinBodySpec#returnResult`() {
+		RestTestClient
+				.bindToController(TestController())
+				.build()
+				.get().uri("/").exchange().expectBody<String>().returnResult()
+				.apply { assertThat(responseBody).isEqualTo("foo") }
+	}
+
+	@Test
+	fun `ResponseSpec#returnResult with reified type parameters`() {
+		responseSpec.returnResult<Foo>()
+		verify { responseSpec.returnResult(object : ParameterizedTypeReference<Foo>() {}) }
+	}
+
+	class Foo
+
+	@RestController
+	class TestController {
+
+		@GetMapping("/")
+		fun home() = "foo"
+
+	}
+
+
+}