Provide access to raw content in RestTestClient

Closes gh-35399

spring-test/src/test/java/org/springframework/test/web/servlet/client/RestTestClientTests.java

@@ -36,6 +36,8 @@ import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.MediaType;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RequestHeader;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RestController;
@@ -317,6 +319,19 @@ class RestTestClientTests {
 					});
 			assertThat(result.getResponseBody().get("uri")).isEqualTo("/test");
 		}
+
+		@Test
+		void testResultContent() {
+			String body = "body-in";
+			EntityExchangeResult<String> result = RestTestClientTests.this.client.post().uri("/body")
+					.body(body)
+					.exchange()
+					.expectStatus().isOk()
+					.expectBody(String.class)
+					.returnResult();
+			assertThat(result.getRequestBodyContent()).isEqualTo(body.getBytes(StandardCharsets.UTF_8));
+			assertThat(result.getResponseBodyContent()).isEqualTo((body + "-out").getBytes(StandardCharsets.UTF_8));
+		}
 	}
 
 
@@ -325,14 +340,20 @@ class RestTestClientTests {
 
 		@RequestMapping(path = {"/test", "/test/*"}, produces = "application/json")
 		public Map<String, Object> handle(
-				@RequestHeader HttpHeaders headers,
-				HttpServletRequest request, HttpServletResponse response) {
+				@RequestHeader HttpHeaders headers, HttpServletRequest request, HttpServletResponse response) {
+
 			response.addCookie(new Cookie("session", "abc"));
+
 			return Map.of(
 					"method", request.getMethod(),
 					"uri", request.getRequestURI(),
 					"headers", headers.toSingleValueMap()
 			);
 		}
+
+		@PostMapping("/body")
+		public String echoBody(@RequestBody String body) {
+			return body + "-out";
+		}
 	}
 }