Update page_title_tag to match JZ's expectations

and add some tests

test/helpers/application_helper_test.rb

@@ -0,0 +1,49 @@
+require "test_helper"
+
+class ApplicationHelperTest < ActionView::TestCase
+  def parse(html)
+    Nokogiri::HTML::DocumentFragment.parse(html)
+  end
+
+  test "page_title_tag on untenanted page" do
+    ApplicationRecord.without_tenant do
+      assert_select parse(page_title_tag), "title", text: "Fizzy"
+    end
+  end
+
+  test "page_title_tag on untenanted page with a page title" do
+    @page_title = "Holodeck"
+
+    ApplicationRecord.without_tenant do
+      assert_select parse(page_title_tag), "title", text: "Holodeck | Fizzy"
+    end
+  end
+
+  test "page_title_tag on tenanted page when user has a single membership" do
+    Current.session = sessions(:david)
+
+    assert_select parse(page_title_tag), "title", text: "Fizzy"
+  end
+
+  test "page_title_tag on tenanted page when user has multiple memberships" do
+    Current.session = sessions(:david)
+    identities(:david).memberships.create!(tenant: "dangling-tenant")
+
+    assert_select parse(page_title_tag), "title", text: "37signals | Fizzy"
+  end
+
+  test "page_title_tag on tenanted page with a page title when user has a single membership" do
+    Current.session = sessions(:david)
+    @page_title = "Holodeck"
+
+    assert_select parse(page_title_tag), "title", text: "Holodeck | Fizzy"
+  end
+
+  test "page_title_tag on tenanted page with a page title when user has multiple memberships" do
+    Current.session = sessions(:david)
+    identities(:david).memberships.create!(tenant: "dangling-tenant")
+    @page_title = "Holodeck"
+
+    assert_select parse(page_title_tag), "title", text: "Holodeck | 37signals | Fizzy"
+  end
+end