Bug fix for assert_template when opening a new session.

See https://github.com/rails/rails/pull/16234#commitcomment-7115670.

actionpack/lib/action_controller/test_case.rb

@@ -12,8 +12,13 @@ module TemplateAssertions
       teardown :teardown_subscriptions
     end
 
+    RENDER_TEMPLATE_INSTANCE_VARIABLES = %w{partials templates layouts files}.freeze
+
     def setup_subscriptions
-      reset_template_assertion
+      RENDER_TEMPLATE_INSTANCE_VARIABLES.each do |instance_variable|
+        instance_variable_set("@_#{instance_variable}", Hash.new(0))
+      end
+
       @_subscribers = []
 
       @_subscribers << ActiveSupport::Notifications.subscribe("render_template.action_view") do |_name, _start, _finish, _id, payload|
@@ -58,10 +63,9 @@ def process(*args)
     end
 
     def reset_template_assertion
-      @_partials = Hash.new(0)
-      @_templates = Hash.new(0)
-      @_layouts = Hash.new(0)
-      @_files = Hash.new(0)
+      RENDER_TEMPLATE_INSTANCE_VARIABLES.each do |instance_variable|
+        instance_variable_get("@_#{instance_variable}").clear
+      end
     end
 
     # Asserts that the request was rendered with the appropriate template file or partials.

actionpack/test/dispatch/template_assertions_test.rb

@@ -55,4 +55,44 @@ def test_assert_file_reset_between_requests
     get '/assert_template/render_nothing'
     assert_template file: nil
   end
+
+  def test_template_reset_between_requests_when_opening_a_session
+    open_session do |session|
+      session.get '/assert_template/render_with_template'
+      session.assert_template 'test/hello_world'
+
+      session.get '/assert_template/render_nothing'
+      session.assert_template nil
+    end
+  end
+
+  def test_partial_reset_between_requests_when_opening_a_session
+    open_session do |session|
+      session.get '/assert_template/render_with_partial'
+      session.assert_template partial: 'test/_partial'
+
+      session.get '/assert_template/render_nothing'
+      session.assert_template partial: nil
+    end
+  end
+
+  def test_layout_reset_between_requests_when_opening_a_session
+    open_session do |session|
+      session.get '/assert_template/render_with_layout'
+      session.assert_template layout: 'layouts/standard'
+
+      session.get '/assert_template/render_nothing'
+      session.assert_template layout: nil
+    end
+  end
+
+  def test_file_reset_between_requests_when_opening_a_session
+    open_session do |session|
+      session.get '/assert_template/render_with_file'
+      session.assert_template file: 'README.rdoc'
+
+      session.get '/assert_template/render_nothing'
+      session.assert_template file: nil
+    end
+  end
 end