fix: Format the error backtrace

Author: rzane

lib/functions_framework/server.rb

@@ -352,7 +352,9 @@ def interpret_response response
         when ::CloudEvents::CloudEventsError
           cloud_events_error_response response
         when ::StandardError
-          error_response "#{response.class}: #{response.message}\n#{response.backtrace}\n"
+          message = "#{response.class}: #{response.message}"
+          message = [message, *response.backtrace].join "\n\t"
+          error_response message
         else
           error_response "Unexpected response type: #{response.class}"
         end

lib/functions_framework/testing.rb

@@ -335,7 +335,8 @@ def interpret_response
           json = ::JSON.dump response
           string_response json, 200, content_type: "application/json"
         when ::StandardError
-          message = "#{response.class}: #{response.message}\n#{response.backtrace}\n"
+          message = "#{response.class}: #{response.message}"
+          message = [message, *response.backtrace].join "\n\t"
           string_response message, 500
         else
           raise "Unexpected response type: #{response.inspect}"

test/test_server.rb

@@ -244,7 +244,7 @@ def query_server_with_retry server
       ::Net::HTTP.get_response URI("#{server_url}/")
     end
     assert_equal "500", response.code
-    assert_match(/Whoops!/, response.body)
+    assert_match(/RuntimeError: Whoops!\n\t#{__FILE__}/, response.body)
     assert_equal "text/plain; charset=utf-8", response["Content-Type"]
   end