Try to handle browser JSON responses more robustly

Adds `assert_json_response` and `json_response` helper method.

Sticking to Capybara's API for getting document text should (in theory)
make this less likely to break in the event of a browser changing how it
renders plain text/JSON responses.

Author: myabc

test/system/alpha/action_menu_test.rb

@@ -7,6 +7,7 @@ class IntegrationActionMenuTest < System::TestCase
     include Primer::ClipboardTestHelpers
     include Primer::JsTestHelpers
     include Primer::KeyboardTestHelpers
+    include Primer::JsonResponseTestHelpers
 
     ###### HELPER METHODS ######
 
@@ -409,9 +410,8 @@ def test_single_select_form_submission
 
       find("input[type=submit]").click
 
-      # for some reason the JSON response is wrapped in HTML, I have no idea why
-      response = JSON.parse(find("pre").text)
-      assert_equal "fast_forward", response["value"]
+      assert_json_response
+      assert_equal "fast_forward", json_response["value"]
     end
 
     def test_single_select_form_uses_label_if_no_value_provided
@@ -422,9 +422,8 @@ def test_single_select_form_uses_label_if_no_value_provided
 
       find("input[type=submit]").click
 
-      # for some reason the JSON response is wrapped in HTML, I have no idea why
-      response = JSON.parse(find("pre").text)
-      assert_equal "Resolve", response["value"]
+      assert_json_response
+      assert_equal "Resolve", json_response["value"]
     end
 
     def test_multiple_select_form_submission
@@ -439,11 +438,10 @@ def test_multiple_select_form_submission
 
       find("input[type=submit]").click
 
-      # for some reason the JSON response is wrapped in HTML, I have no idea why
-      response = JSON.parse(find("pre").text)
+      assert_json_response
 
       # "ours" is pre-selected
-      assert_equal %w[fast_forward recursive ours], response["value"]
+      assert_equal %w[fast_forward recursive ours], json_response["value"]
     end
 
     def test_multiple_select_form_uses_label_if_no_value_provided
@@ -458,11 +456,10 @@ def test_multiple_select_form_uses_label_if_no_value_provided
 
       find("input[type=submit]").click
 
-      # for some reason the JSON response is wrapped in HTML, I have no idea why
-      response = JSON.parse(find("pre").text)
+      assert_json_response
 
       # "ours" is pre-selected
-      assert_equal %w[fast_forward ours Resolve], response["value"]
+      assert_equal %w[fast_forward ours Resolve], json_response["value"]
     end
 
     def test_multiple_select_does_not_set_dynamic_label_for_preselected_item
@@ -476,8 +473,8 @@ def test_individual_items_can_submit_post_requests_via_forms
       click_on_invoker_button
       click_on_fourth_item
 
-      response = JSON.parse(find("pre").text)
-      assert_equal "bar", response["value"]
+      assert_json_response
+      assert_equal "bar", json_response["value"]
     end
 
     def test_single_select_items_can_submit_forms
@@ -486,9 +483,8 @@ def test_single_select_items_can_submit_forms
       click_on_invoker_button
       click_on_first_item
 
-      # for some reason the JSON response is wrapped in HTML, I have no idea why
-      response = JSON.parse(find("pre").text)
-      assert_equal "group-by-repository", response["value"]
+      assert_json_response
+      assert_equal "group-by-repository", json_response["value"]
     end
 
     def test_single_select_items_can_submit_forms_on_enter
@@ -499,9 +495,8 @@ def test_single_select_items_can_submit_forms_on_enter
       # "click" first item
       keyboard.type(:enter)
 
-      # for some reason the JSON response is wrapped in HTML, I have no idea why
-      response = JSON.parse(find("pre").text)
-      assert_equal "group-by-repository", response["value"]
+      assert_json_response
+      assert_equal "group-by-repository", json_response["value"]
     end
 
     def test_single_select_items_can_submit_forms_on_keydown_space
@@ -512,9 +507,8 @@ def test_single_select_items_can_submit_forms_on_keydown_space
       # "click" first item
       keyboard.type(:space)
 
-      # for some reason the JSON response is wrapped in HTML, I have no idea why
-      response = JSON.parse(find("pre").text)
-      assert_equal "group-by-repository", response["value"]
+      assert_json_response
+      assert_equal "group-by-repository", json_response["value"]
     end
 
     def test_single_select_items_can_submit_forms_with_multiple_fields
@@ -523,9 +517,8 @@ def test_single_select_items_can_submit_forms_with_multiple_fields
       click_on_invoker_button
       click_on_first_item
 
-      # for some reason the JSON response is wrapped in HTML, I have no idea why
-      response = JSON.parse(find("pre").text)
-      assert_equal "query", response.dig("other_params", "query")
+      assert_json_response
+      assert_equal "query", json_response.dig("other_params", "query")
     end
 
     def test_deferred_loading

test/system/alpha/select_panel_test.rb

@@ -7,6 +7,7 @@ module Alpha
   class IntegrationSelectPanelTest < System::TestCase
     include Primer::KeyboardTestHelpers
     include Primer::JsTestHelpers
+    include Primer::JsonResponseTestHelpers
 
     ###### HELPER METHODS ######
 
@@ -1221,9 +1222,8 @@ def test_single_select_form
 
       click_on "Submit"
 
-      # for some reason the JSON response is wrapped in HTML, I have no idea why
-      response = JSON.parse(find("pre").text)
-      assert_equal "item2", response.dig(*%w(form_params item))
+      assert_json_response
+      assert_equal "item2", json_response.dig(*%w(form_params item))
     end
 
     def test_single_select_form_submits_pre_selected_item
@@ -1232,9 +1232,8 @@ def test_single_select_form_submits_pre_selected_item
       # the first item has been pre-selected, so there's no need to select any items
       click_on "Submit"
 
-      # for some reason the JSON response is wrapped in HTML, I have no idea why
-      response = JSON.parse(find("pre").text)
-      assert_equal "item1", response.dig(*%w(form_params item))
+      assert_json_response
+      assert_equal "item1", json_response.dig(*%w(form_params item))
     end
 
     def test_multi_select_form
@@ -1246,11 +1245,10 @@ def test_multi_select_form
 
       click_on "Submit"
 
-      # for some reason the JSON response is wrapped in HTML, I have no idea why
-      response = JSON.parse(find("pre").text)
+      assert_json_response
 
       # first item is pre-selected
-      assert_equal ["item1", "item2"], response.dig(*%w(form_params item))
+      assert_equal ["item1", "item2"], json_response.dig(*%w(form_params item))
     end
 
     ########## ANNOUNCEMENT TESTS ############

test/test_helper.rb

@@ -25,6 +25,7 @@
 require "test_helpers/mouse_test_helpers"
 require "test_helpers/js_test_helpers"
 require "test_helpers/window_test_helpers"
+require "test_helpers/json_response_test_helpers"
 require "action_controller/railtie"
 require "rails/test_unit/railtie"
 require "active_model/railtie"

test/test_helpers/json_response_test_helpers.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+module Primer
+  module JsonResponseTestHelpers
+    def assert_json_response
+      assert_current_path(/\.json$/)
+      assert_equal json_mime_type, page.evaluate_script("document.contentType")
+    end
+
+    def json_response
+      @json_response ||= JSON.parse(page.document.text)
+    end
+
+    private
+
+    def json_mime_type
+      @json_mime_type ||= Mime::Type.lookup("application/json")
+    end
+  end
+end