Fix response request in MockClient (#657)

Use the stub returned request field from the response.

Author: teodor-appd

CHANGELOG.md

@@ -1,6 +1,9 @@
 ## 0.13.5-dev
 
 * Allow async callbacks in RetryClient.
+* In `MockHttpClient` use the callback returned `Response.request` instead of
+  the argument value to give more control to the callback. This may be breaking
+  for callbacks which return incomplete Responses and relied on the default.
 
 ## 0.13.4
 

lib/src/mock_client.dart

@@ -43,7 +43,7 @@ class MockClient extends BaseClient {
           return StreamedResponse(
               ByteStream.fromBytes(response.bodyBytes), response.statusCode,
               contentLength: response.contentLength,
-              request: baseRequest,
+              request: response.request,
               headers: response.headers,
               isRedirect: response.isRedirect,
               persistentConnection: response.persistentConnection,
@@ -57,7 +57,7 @@ class MockClient extends BaseClient {
           final response = await fn(request, bodyStream);
           return StreamedResponse(response.stream, response.statusCode,
               contentLength: response.contentLength,
-              request: request,
+              request: response.request,
               headers: response.headers,
               isRedirect: response.isRedirect,
               persistentConnection: response.persistentConnection,