Show error message for API 500 error in tests, and

document have_gitlab_http_status

doc/development/testing.md

@@ -270,6 +270,15 @@ complexity of RSpec expectations.They should be placed under
 a certain type of specs only (e.g. features, requests etc.) but shouldn't be if
 they apply to multiple type of specs.
 
+#### have_gitlab_http_status
+
+Prefer `have_gitlab_http_status` over `have_http_status` because the former
+could also show the response body whenever the status mismatched. This would
+be very useful whenever some tests start breaking and we would love to know
+why without editing the source and rerun the tests.
+
+This is especially useful whenever it's showing 500 internal server error.
+
 ### Shared contexts
 
 All shared contexts should be be placed under `spec/support/shared_contexts/`.

lib/api/helpers.rb

@@ -257,7 +257,15 @@ module API
       message << "  " << trace.join("\n  ")
 
       API.logger.add Logger::FATAL, message
-      rack_response({ 'message' => '500 Internal Server Error' }.to_json, 500)
+
+      response_message =
+        if Rails.env.test?
+          message
+        else
+          '500 Internal Server Error'
+        end
+
+      rack_response({ 'message' => response_message }.to_json, 500)
     end
 
     # project helpers