DEV: Unskip system tests and avoid predicate matchers (#224)

RSpec predicate matchers provide poor output when tests fail.
This commit switches to Capybara RSpec matches so that we get more
debugging information as to why these tests are flaky...

spec/system/admin_update_spec.rb

@@ -4,25 +4,16 @@ require_dependency "docker_manager/git_repo"
 
 RSpec.describe "Admin update", type: :system do
   fab!(:admin)
-  let(:au_page) { PageObjects::Pages::AdminUpdate.new }
+  let(:admin_update_page) { PageObjects::Pages::AdminUpdate.new }
 
-  before do
-    sign_in(admin)
-    au_page.visit
-  end
+  before { sign_in(admin) }
 
-  # flaky test /t/133037
-  xit "shows the update page" do
-    expect(au_page).to be_displayed
-  end
+  it "displays the admin update page with the right respositories" do
+    visit("/admin/update")
 
-  # flaky test /t/133033
-  xit "shows the core repo" do
-    expect(au_page).to have_repo(name: "Discourse")
-  end
-
-  # flaky test /t/133032
-  xit "shows the docker_manager plugin repo" do
-    expect(au_page).to have_repo(name: "Docker Manager", url: "https://meta.discourse.org/t/12655")
+    expect(page).to have_css("h3", exact_text: I18n.t("js.admin.docker.update_title"))
+    expect(page).to have_css("tr.repo .repo__name", exact_text: "Discourse")
+    expect(page).to have_css("tr.repo .repo__name", exact_text: "Docker Manager")
+    expect(page).to have_css("tr.repo .repo__about a[href='https://meta.discourse.org/t/12655']")
   end
 end

spec/system/page_objects/pages/admin_update.rb

@@ -1,21 +0,0 @@
-# frozen_string_literal: true
-
-module PageObjects
-  module Pages
-    class AdminUpdate < PageObjects::Pages::Base
-      def visit
-        page.visit("/admin/update")
-        self
-      end
-
-      def displayed?
-        has_css?("h3", text: "Updates")
-      end
-
-      def has_repo?(repo)
-        has_css?("tr.repo .repo__name", text: repo[:name]) &&
-          (!repo[:url] || has_css?("tr.repo .repo__about a[href='#{repo[:url]}']"))
-      end
-    end
-  end
-end