Disallow pending cops

While we don't want to blindly enable all new cops, we should take a
stance on all cops, so our consumers don't have to.

Therefore, no cops should be marked as pending. When a Rubocop bump
introduces a new cop, we should triage it and either explicitly enable
or disable it.

If, for some reason, an update is required during a bad time for triage,
the updater should open an triage issue and mark the cop as disabled until it
is triaged.

Author: sambostock

test/config_test.rb

@@ -6,12 +6,14 @@
 require "rake"
 
 class ConfigTest < Minitest::Test
+  FULL_CONFIG_PATH = "test/fixtures/full_config.yml"
+
   def test_config_is_unchanged
     skip if checking_rubocop_version_compatibility?
 
     Rake.application.load_rakefile
 
-    original_config = "test/fixtures/full_config.yml"
+    original_config = FULL_CONFIG_PATH
 
     Tempfile.create do |tempfile|
       Rake::Task["config:dump"].invoke(tempfile.path)
@@ -70,6 +72,25 @@ def test_config_is_sorted_alphabetically
     assert_sorted(following_keys, "Keys after AllCops in rubocop.yml must be sorted")
   end
 
+  def test_no_cops_are_configured_as_pending
+    pending_cops = []
+
+    load_method = YAML.respond_to?(:unsafe_load_file) ? :unsafe_load_file : :load_file
+    YAML.public_send(load_method, FULL_CONFIG_PATH).each do |cop_name, cop_config|
+      pending_cops << cop_name if Hash === cop_config && cop_config["Enabled"] == "pending"
+    end
+
+    assert(pending_cops.empty?, <<~ERROR_MESSAGE.chomp)
+      Error: The style guide should take a stance on all cops, but following cops are marked as pending:
+
+      #{pending_cops.map { "    #{_1}:\n      Enabled: pending" }.join("\n\n")}
+
+      Please update the config to mark all of the these cops as either `Enabled: true` or `Enabled: false`
+
+      If this is a bad time to triage, please open an issue, and mark them as `Enabled: false` for now.
+    ERROR_MESSAGE
+  end
+
   private
 
   def checking_rubocop_version_compatibility?