Introduce a new middleware for the test environment that can block requests

Gemfile

@@ -327,6 +327,7 @@ group :test do
   gem 'test_after_commit', '~> 1.1'
   gem 'sham_rack', '~> 1.3.6'
   gem 'timecop', '~> 0.8.0'
+  gem 'concurrent-ruby', '~> 1.0.5'
 end
 
 gem 'octokit', '~> 4.6.2'

Gemfile.lock

@@ -128,7 +128,7 @@ GEM
       execjs
     coffee-script-source (1.10.0)
     colorize (0.7.7)
-    concurrent-ruby (1.0.4)
+    concurrent-ruby (1.0.5)
     connection_pool (2.2.1)
     crack (0.4.3)
       safe_yaml (~> 1.0.0)
@@ -868,6 +868,7 @@ DEPENDENCIES
   chronic (~> 0.10.2)
   chronic_duration (~> 0.10.6)
   coffee-rails (~> 4.1.0)
+  concurrent-ruby (~> 1.0.5)
   connection_pool (~> 2.0)
   creole (~> 0.5.0)
   d3_rails (~> 3.5.0)

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')
+
   # Settings specified here will take precedence over those in config/application.rb
 
   # The test environment is used exclusively to run your application's

lib/gitlab/testing/request_blocker_middleware.rb

+# rubocop:disable Style/ClassVars
+
+# This is inspired by http://www.salsify.com/blog/engineering/tearing-capybara-ajax-tests
+# Rack middleware that keeps track of the number of active requests and can block new requests.
+module Gitlab
+  module Testing
+    class RequestBlockerMiddleware
+      @@num_active_requests = Concurrent::AtomicFixnum.new(0)
+      @@block_requests = Concurrent::AtomicBoolean.new(false)
+
+      # Returns the number of requests the server is currently processing.
+      def self.num_active_requests
+        @@num_active_requests.value
+      end
+
+      # Prevents the server from accepting new requests. Any new requests will return an HTTP
+      # 503 status.
+      def self.block_requests!
+        @@block_requests.value = true
+      end
+
+      # Allows the server to accept requests again.
+      def self.allow_requests!
+        @@block_requests.value = false
+      end
+
+      def initialize(app)
+        @app = app
+      end
+
+      def call(env)
+        increment_active_requests
+        if block_requests?
+          block_request(env)
+        else
+          @app.call(env)
+        end
+      ensure
+        decrement_active_requests
+      end
+
+      private
+
+      def block_requests?
+        @@block_requests.true?
+      end
+
+      def block_request(env)
+        [503, {}, []]
+      end
+
+      def increment_active_requests
+        @@num_active_requests.increment
+      end
+
+      def decrement_active_requests
+        @@num_active_requests.decrement
+      end
+    end
+  end
+end

spec/spec_helper.rb

@@ -35,6 +35,7 @@ RSpec.configure do |config|
   config.include Warden::Test::Helpers, type: :request
   config.include LoginHelpers, type: :feature
   config.include SearchHelpers, type: :feature
+  config.include WaitForRequests, :js
   config.include WaitForAjax, type: :feature
   config.include StubConfiguration
   config.include EmailHelpers, type: :mailer

spec/support/wait_for_requests.rb

+module WaitForRequests
+  extend self
+
+  # This is inspired by http://www.salsify.com/blog/engineering/tearing-capybara-ajax-tests
+  def wait_for_requests_complete
+    stop_client
+    Gitlab::Testing::RequestBlockerMiddleware.block_requests!
+    wait_for('pending AJAX requests complete') do
+      Gitlab::Testing::RequestBlockerMiddleware.num_active_requests.zero?
+    end
+  ensure
+    Gitlab::Testing::RequestBlockerMiddleware.allow_requests!
+  end
+
+  # Navigate away from the current page which will prevent any new requests from being started
+  def stop_client
+    page.execute_script %Q{
+      window.location = "about:blank";
+    }
+  end
+
+  # Waits until the passed block returns true
+  def wait_for(condition_name, max_wait_time: Capybara.default_max_wait_time, polling_interval: 0.01)
+    wait_until = Time.now + max_wait_time.seconds
+    loop do
+      break if yield
+      if Time.now > wait_until
+        raise "Condition not met: #{condition_name}"
+      else
+        sleep(polling_interval)
+      end
+    end
+  end
+end
+
+RSpec.configure do |config|
+  config.after(:each, :js) do
+    wait_for_requests_complete
+  end
+end