implement basic request inspector for use in Capybara tests

config/environments/test.rb

 Rails.application.configure do
   # Make sure the middleware is inserted first in middleware chain
   config.middleware.insert_before('ActionDispatch::Static', 'Gitlab::Testing::RequestBlockerMiddleware')
+  config.middleware.insert_before('ActionDispatch::Static', 'Gitlab::Testing::RequestInspectorMiddleware')
 
   # Settings specified here will take precedence over those in config/application.rb
 

lib/gitlab/testing/request_inspector_middleware.rb

+module Gitlab
+  module Testing
+    class RequestInspectorMiddleware
+      @@log_requests = Concurrent::AtomicBoolean.new(false)
+      @@logged_requests = Concurrent::Array.new
+
+      # Resets the current request log and starts logging requests
+      def self.log_requests!
+        @@logged_requests.replace([])
+        @@log_requests.value = true
+      end
+
+      # Stops logging requests
+      def self.stop_logging!
+        @@log_requests.value = false
+      end
+
+      def self.requests
+        @@logged_requests
+      end
+
+      def initialize(app)
+        @app = app
+      end
+
+      def call(env)
+        return @app.call(env) unless @@log_requests.true?
+
+        url = env['REQUEST_URI']
+        request_headers = env_http_headers(env)
+        status, headers, body = @app.call(env)
+
+        log_response({
+          url: url,
+          status_code: status,
+          request_headers: request_headers,
+          response_headers: headers
+        })
+
+        [status, headers, body]
+      end
+
+      private
+
+      def env_http_headers(env)
+        Hash[*env.select {|k,v| k.start_with? 'HTTP_'}
+          .collect {|k,v| [k.sub(/^HTTP_/, ''), v]}
+          .collect {|k,v| [k.split('_').collect(&:capitalize).join('-'), v]}
+          .sort
+          .flatten]
+      end
+
+      def log_response(response)
+        @@logged_requests.push(response)
+        STDOUT.puts response.to_json
+      end
+    end
+  end
+end