Replace delegated predicate methods with boolean-returning methods

Predicate methods should return a boolean value, however when we
delegate with allow_nil to properly handle non-extant relations, we
end up with true, false, and nil as possible responses. While we
generally are loose about nil being equivalent to false in Ruby, I
feel like a predicate method is a special signal that we very much
care about the boolean nature of its response.

ee/app/models/ee/project.rb

@@ -197,10 +197,6 @@ module EE
 
       delegate :ci_minutes_quota, to: :shared_runners_limit_namespace
 
-      delegate :last_update_succeeded?, :last_update_failed?,
-        :ever_updated_successfully?, :hard_failed?,
-        to: :import_state, prefix: :mirror, allow_nil: true
-
       delegate :merge_pipelines_enabled, :merge_pipelines_enabled=, :merge_pipelines_enabled?, :merge_pipelines_were_disabled?, to: :ci_cd_settings
       delegate :merge_trains_enabled, :merge_trains_enabled=, :merge_trains_enabled?, to: :ci_cd_settings
 
@@ -256,6 +252,22 @@ module EE
       end
     end
 
+    def mirror_last_update_succeeded?
+      !!import_state&.last_update_succeeded?
+    end
+
+    def mirror_last_update_failed?
+      !!import_state&.last_update_failed?
+    end
+
+    def mirror_ever_updated_successfully?
+      !!import_state&.ever_updated_successfully?
+    end
+
+    def mirror_hard_failed?
+      !!import_state&.hard_failed?
+    end
+
     class_methods do
       extend ::Gitlab::Utils::Override
 

ee/spec/models/project_spec.rb

@@ -125,6 +125,46 @@ RSpec.describe Project do
       end
     end
 
+    context 'import_state dependant predicate method' do
+      shared_examples 'returns expected values' do
+        context 'when project lacks a import_state relation' do
+          it 'returns false' do
+            expect(project.send("mirror_#{method}")).to be_falsey
+          end
+        end
+
+        context 'when project has a import_state relation' do
+          before do
+            create(:import_state, project: project)
+          end
+
+          it 'accesses the value from the import_state' do
+            expect(project.import_state).to receive(method)
+
+            project.send("mirror_#{method}")
+          end
+        end
+      end
+
+      describe '#mirror_last_update_succeeded?' do
+        it_behaves_like 'returns expected values' do
+          let(:method) { "last_update_succeeded?" }
+        end
+      end
+
+      describe '#mirror_last_update_failed?' do
+        it_behaves_like 'returns expected values' do
+          let(:method) { "last_update_failed?" }
+        end
+      end
+
+      describe '#mirror_ever_updated_successfully?' do
+        it_behaves_like 'returns expected values' do
+          let(:method) { "ever_updated_successfully?" }
+        end
+      end
+    end
+
     describe 'approval_rules association' do
       let_it_be(:rule, reload: true) { create(:approval_project_rule) }
       let(:project) { rule.project }