diff --git a/spring-test/src/main/java/org/springframework/mock/http/client/reactive/MockClientHttpResponse.java b/spring-test/src/main/java/org/springframework/mock/http/client/reactive/MockClientHttpResponse.java
index 9385899bff..739d8ba935 100644
--- a/spring-test/src/main/java/org/springframework/mock/http/client/reactive/MockClientHttpResponse.java
+++ b/spring-test/src/main/java/org/springframework/mock/http/client/reactive/MockClientHttpResponse.java
@@ -148,4 +148,10 @@ public class MockClientHttpResponse implements ClientHttpResponse {
 		return (charset != null ? charset : StandardCharsets.UTF_8);
 	}
 
+
+	@Override
+	public String toString() {
+		HttpStatus code = HttpStatus.resolve(this.status);
+		return (code != null ? code.name() + "(" + this.status + ")" : "Status (" + this.status + ")") + this.headers;
+	}
 }
diff --git a/spring-test/src/main/java/org/springframework/test/web/reactive/server/HttpHandlerConnector.java b/spring-test/src/main/java/org/springframework/test/web/reactive/server/HttpHandlerConnector.java
index 792e3c5307..c5841c41ec 100644
--- a/spring-test/src/main/java/org/springframework/test/web/reactive/server/HttpHandlerConnector.java
+++ b/spring-test/src/main/java/org/springframework/test/web/reactive/server/HttpHandlerConnector.java
@@ -83,7 +83,9 @@ public class HttpHandlerConnector implements ClientHttpConnector {
 	private Mono<ClientHttpResponse> doConnect(
 			HttpMethod httpMethod, URI uri, Function<? super ClientHttpRequest, Mono<Void>> requestCallback) {
 
-		MonoProcessor<ClientHttpResponse> result = MonoProcessor.create();
+		MonoProcessor<Void> requestWriteCompletion = MonoProcessor.create();
+		MonoProcessor<Void> handlerCompletion = MonoProcessor.create();
+		ClientHttpResponse[] savedResponse = new ClientHttpResponse[1];
 
 		MockClientHttpRequest mockClientRequest = new MockClientHttpRequest(httpMethod, uri);
 		MockServerHttpResponse mockServerResponse = new MockServerHttpResponse();
@@ -92,20 +94,26 @@ public class HttpHandlerConnector implements ClientHttpConnector {
 			log("Invoking HttpHandler for ", httpMethod, uri);
 			ServerHttpRequest mockServerRequest = adaptRequest(mockClientRequest, requestBody);
 			ServerHttpResponse responseToUse = prepareResponse(mockServerResponse, mockServerRequest);
-			this.handler.handle(mockServerRequest, responseToUse).subscribe(aVoid -> {}, result::onError);
+			this.handler.handle(mockServerRequest, responseToUse).subscribe(handlerCompletion);
 			return Mono.empty();
 		});
 
 		mockServerResponse.setWriteHandler(responseBody ->
 				Mono.fromRunnable(() -> {
 					log("Creating client response for ", httpMethod, uri);
-					result.onNext(adaptResponse(mockServerResponse, responseBody));
+					savedResponse[0] = adaptResponse(mockServerResponse, responseBody);
 				}));
 
 		log("Writing client request for ", httpMethod, uri);
-		requestCallback.apply(mockClientRequest).subscribe(aVoid -> {}, result::onError);
+		requestCallback.apply(mockClientRequest).subscribe(requestWriteCompletion);
 
-		return result;
+		return Mono.when(requestWriteCompletion, handlerCompletion)
+				.onErrorMap(ex -> {
+					ClientHttpResponse response = savedResponse[0];
+					return response != null ? new FailureAfterResponseCompletedException(response, ex) : ex;
+				})
+				.then(Mono.fromCallable(() -> savedResponse[0] != null ?
+						savedResponse[0] : adaptResponse(mockServerResponse, Flux.empty())));
 	}
 
 	private void log(String message, HttpMethod httpMethod, URI uri) {
@@ -135,4 +143,33 @@ public class HttpHandlerConnector implements ClientHttpConnector {
 		return clientResponse;
 	}
 
+
+	/**
+	 * Indicates that an error occurred after the server response was completed,
+	 * via {@link ServerHttpResponse#writeWith} or {@link ServerHttpResponse#setComplete()},
+	 * and can no longer be changed. This exception wraps the error and also
+	 * provides {@link #getCompletedResponse() access} to the response.
+	 * <p>What happens on an actual running server depends on when the server
+	 * commits the response and the error may or may not change the response.
+	 * Therefore in tests without a server the exception is wrapped and allowed
+	 * to propagate so the application is alerted.
+	 * @since 5.2.2
+	 */
+	@SuppressWarnings("serial")
+	public static final class FailureAfterResponseCompletedException extends RuntimeException {
+
+		private final ClientHttpResponse completedResponse;
+
+
+		private FailureAfterResponseCompletedException(ClientHttpResponse response, Throwable cause) {
+			super("Error occurred after response was completed: " + response, cause);
+			this.completedResponse = response;
+		}
+
+
+		public ClientHttpResponse getCompletedResponse() {
+			return this.completedResponse;
+		}
+	}
+
 }
diff --git a/spring-web/src/test/java/org/springframework/mock/http/client/reactive/test/MockClientHttpResponse.java b/spring-web/src/test/java/org/springframework/mock/http/client/reactive/test/MockClientHttpResponse.java
index f7b772a74c..e757bfad7c 100644
--- a/spring-web/src/test/java/org/springframework/mock/http/client/reactive/test/MockClientHttpResponse.java
+++ b/spring-web/src/test/java/org/springframework/mock/http/client/reactive/test/MockClientHttpResponse.java
@@ -64,7 +64,7 @@ public class MockClientHttpResponse implements ClientHttpResponse {
 	}
 
 	public MockClientHttpResponse(int status) {
-		Assert.isTrue(status >= 100 && status < 600, "Status must be between 1xx and 5xx");
+		Assert.isTrue(status > 99 && status < 1000, "Status must be between 100 and 999");
 		this.status = status;
 	}
 
@@ -148,4 +148,10 @@ public class MockClientHttpResponse implements ClientHttpResponse {
 		return (charset != null ? charset : StandardCharsets.UTF_8);
 	}
 
+
+	@Override
+	public String toString() {
+		HttpStatus code = HttpStatus.resolve(this.status);
+		return (code != null ? code.name() + "(" + this.status + ")" : "Status (" + this.status + ")") + this.headers;
+	}
 }