test: backfill hotkeys helper tests

and remove support for the unused use case of comma-delimited-strings

test/helpers/hotkeys_helper_test.rb

@@ -0,0 +1,52 @@
+require "test_helper"
+
+class HotkeysHelperTest < ActionView::TestCase
+  include SetPlatform
+
+  test "mac modifier key" do
+    emulate_mac
+
+    assert_equal "⌘J", hotkey_label([ "⌘", "J" ])
+  end
+
+  test "linux modifier key" do
+    emulate_linux
+
+    assert_equal "ctrlJ", hotkey_label([ "ctrl", "J" ])
+  end
+
+  test "mac enter" do
+    emulate_mac
+
+    assert_equal "returnJ", hotkey_label([ "enter", "J" ])
+  end
+
+  test "linux enter" do
+    emulate_linux
+
+    assert_equal "enterJ", hotkey_label([ "enter", "J" ])
+  end
+
+  test "mac hyper" do
+    emulate_mac
+
+    assert_equal "hyperJ", hotkey_label([ "hyper", "J" ])
+  end
+
+  test "linux hyper" do
+    emulate_linux
+
+    assert_equal "hyperJ", hotkey_label([ "hyper", "J" ])
+  end
+
+  private
+    def emulate_mac
+      stub_platform = ApplicationPlatform.new("Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.114 Safari/537.36")
+      self.stubs(:platform).returns(stub_platform)
+    end
+
+    def emulate_linux
+      stub_platform = ApplicationPlatform.new("Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.114 Safari/537.36")
+      self.stubs(:platform).returns(stub_platform)
+    end
+end