3 files changed, 48 insertions, 6 deletions

diff --git a/actionpack/test/controller/integration_test.rb b/actionpack/test/controller/integration_test.rb
index caacd66bd6..4f5f5b71ae 100644
--- a/actionpack/test/controller/integration_test.rb
+++ b/actionpack/test/controller/integration_test.rb
@@ -543,6 +543,32 @@ class IntegrationProcessTest < ActionDispatch::IntegrationTest
     end
   end
 
+  def test_setting_vary_header_when_request_is_xhr_with_accept_header
+    with_test_route_set do
+      get "/get", headers: { "Accept" => "application/json" }, xhr: true
+      assert_equal "Accept", response.headers["Vary"]
+    end
+  end
+
+  def test_not_setting_vary_header_when_format_is_provided
+    with_test_route_set do
+      get "/get", params: { format: "json" }
+      assert_nil response.headers["Vary"]
+    end
+  end
+
+  def test_not_setting_vary_header_when_ignore_accept_header_is_set
+    original_ignore_accept_header = ActionDispatch::Request.ignore_accept_header
+    ActionDispatch::Request.ignore_accept_header = true
+
+    with_test_route_set do
+      get "/get", headers: { "Accept" => "application/json" }, xhr: true
+      assert_nil response.headers["Vary"]
+    end
+  ensure
+    ActionDispatch::Request.ignore_accept_header = original_ignore_accept_header
+  end
+
   private
     def with_default_headers(headers)
       original = ActionDispatch::Response.default_headers
@@ -580,7 +606,7 @@ class MetalIntegrationTest < ActionDispatch::IntegrationTest
 
   class Poller
     def self.call(env)
-      if env["PATH_INFO"] =~ /^\/success/
+      if /^\/success/.match?(env["PATH_INFO"])
         [200, { "Content-Type" => "text/plain", "Content-Length" => "12" }, ["Hello World!"]]
       else
         [404, { "Content-Type" => "text/plain", "Content-Length" => "0" }, []]
diff --git a/actionpack/test/controller/log_subscriber_test.rb b/actionpack/test/controller/log_subscriber_test.rb
index 1a7e7f6cbb..46ab7b4f74 100644
--- a/actionpack/test/controller/log_subscriber_test.rb
+++ b/actionpack/test/controller/log_subscriber_test.rb
@@ -139,7 +139,7 @@ class ACLogSubscriberTest < ActionController::TestCase
   def test_process_action_without_parameters
     get :show
     wait
-    assert_nil logs.detect { |l| l =~ /Parameters/ }
+    assert_nil logs.detect { |l| /Parameters/.match?(l) }
   end
 
   def test_process_action_with_parameters
diff --git a/actionpack/test/controller/render_test.rb b/actionpack/test/controller/render_test.rb
index a2a6c69dd3..dd76824413 100644
--- a/actionpack/test/controller/render_test.rb
+++ b/actionpack/test/controller/render_test.rb
@@ -4,6 +4,11 @@ require "abstract_unit"
 require "controller/fake_models"
 
 class TestControllerWithExtraEtags < ActionController::Base
+  self.view_paths = [ActionView::FixtureResolver.new(
+    "test/with_implicit_template.erb" => "Hello explicitly!",
+    "test/hello_world.erb" => "Hello world!"
+  )]
+
   def self.controller_name; "test"; end
   def self.controller_path; "test"; end
 
@@ -37,6 +42,11 @@ class TestControllerWithExtraEtags < ActionController::Base
 end
 
 class ImplicitRenderTestController < ActionController::Base
+  self.view_paths = [ActionView::FixtureResolver.new(
+    "implicit_render_test/hello_world.erb" => "Hello world!",
+    "implicit_render_test/empty_action_with_template.html.erb" => "<h1>Empty action rendered this implicitly.</h1>\n"
+  )]
+
   def empty_action
   end
 
@@ -46,6 +56,10 @@ end
 
 module Namespaced
   class ImplicitRenderTestController < ActionController::Base
+    self.view_paths = [ActionView::FixtureResolver.new(
+      "namespaced/implicit_render_test/hello_world.erb" => "Hello world!"
+    )]
+
     def hello_world
       fresh_when(etag: "abc")
     end
@@ -293,13 +307,15 @@ end
 module TemplateModificationHelper
   private
     def modify_template(name)
-      path = File.expand_path("../fixtures/#{name}.erb", __dir__)
-      original = File.read(path)
-      File.write(path, "#{original} Modified!")
+      hash = @controller.view_paths.first.instance_variable_get(:@hash)
+      key = name + ".erb"
+      original = hash[key]
+      hash[key] = "#{original} Modified!"
       ActionView::LookupContext::DetailsKey.clear
       yield
     ensure
-      File.write(path, original)
+      hash[key] = original
+      ActionView::LookupContext::DetailsKey.clear
     end
 end