Configures tests to minimize flackyness

Reference: https://bibwild.wordpress.com/2016/02/18/struggling-towards-reliable-capybara-javascript-testing/

The only thing I did not do was removing the random order in the tests.

config/environments/test.rb

@@ -10,7 +10,12 @@ Rails.application.configure do
   # Do not eager load code on boot. This avoids loading your whole application
   # just for the purpose of running a single test. If you are using a tool that
   # preloads Rails for running tests, you may have to set it to true.
-  config.eager_load = false
+  config.eager_load = true
+
+  # Setting allow_corrency to false tells rails to force every request to
+  # "wait in line", serving one after the other
+  # Setting eager_load to true also sets allow_concurrency to true.
+  config.allow_concurrency = false
 
   # Configure static file server for tests with Cache-Control for performance.
   config.serve_static_files   = true

spec/rails_helper.rb

@@ -19,6 +19,9 @@ ActiveRecord::Migration.maintain_test_schema!
 
 RSpec.configure do |config|
   config.infer_spec_type_from_file_location!
+  config.after :each do
+    Warden.test_reset!
+  end
 end
 
 Capybara.javascript_driver = :poltergeist

spec/spec_helper.rb

@@ -18,14 +18,46 @@ RSpec.configure do |config|
     DatabaseCleaner.clean_with :truncation
   end
 
+  config.before(:suite) do
+    if config.use_transactional_fixtures?
+      raise(<<-MSG)
+        Delete line `config.use_transactional_fixtures = true` from rails_helper.rb
+        (or set it to false) to prevent uncommitted transactions being used in
+        JavaScript-dependent specs.
+
+        During testing, the app-under-test that the browser driver connects to
+        uses a different database connection to the database connection used by
+        the spec. The app's database connection would not be able to access
+        uncommitted transaction data setup over the spec's database connection.
+      MSG
+    end
+    DatabaseCleaner.clean_with(:truncation)
+  end
+
   config.before(:each) do |example|
-    DatabaseCleaner.strategy = example.metadata[:js] ? :truncation : :transaction
-    DatabaseCleaner.start
+    DatabaseCleaner.strategy = :transaction
     I18n.locale = :en
     load "#{Rails.root}/db/seeds.rb"
   end
 
-  config.after(:each) do
+  config.before(:each, type: :feature) do
+    # :rack_test driver's Rack app under test shares database connection
+    # with the specs, so continue to use transaction strategy for speed.
+    driver_shares_db_connection_with_specs = Capybara.current_driver == :rack_test
+
+    if !driver_shares_db_connection_with_specs
+      # Driver is probably for an external browser with an app
+      # under test that does *not* share a database connection with the
+      # specs, so use truncation strategy.
+      DatabaseCleaner.strategy = :truncation
+    end
+  end
+
+  config.before(:each) do
+    DatabaseCleaner.start
+  end
+
+  config.append_after(:each) do
     DatabaseCleaner.clean
   end