Clean up specs according to testing guidelines

spec/models/ci/pipeline_spec.rb

@@ -3442,14 +3442,15 @@ RSpec.describe Ci::Pipeline, :mailer, factory_default: :keep do
   end
 
   describe "#builds_with_coverage" do
-    let!(:rspec) { create(:ci_build, name: 'rspec', coverage: 97.1, pipeline: pipeline) }
-    let!(:jest) { create(:ci_build, name: 'jest', coverage: 94.1, pipeline: pipeline) }
-    let!(:karma) { create(:ci_build, name: 'karma', coverage: nil, pipeline: pipeline) }
+    it 'returns builds with coverage only' do
+      rspec = create(:ci_build, name: 'rspec', coverage: 97.1, pipeline: pipeline)
+      jest  = create(:ci_build, name: 'jest', coverage: 94.1, pipeline: pipeline)
+      karma = create(:ci_build, name: 'karma', coverage: nil, pipeline: pipeline)
 
-    subject(:builds) { pipeline.builds_with_coverage }
+      builds = pipeline.builds_with_coverage
 
-    it 'returns builds with coverage only' do
-      expect(builds).to match_array([rspec, jest])
+      expect(builds).to include(rspec, jest)
+      expect(builds).not_to include(karma)
     end
   end
 end

spec/models/merge_request_spec.rb

@@ -4114,8 +4114,8 @@ RSpec.describe MergeRequest, factory_default: :keep do
   end
 
   describe '#head_pipeline_builds_with_coverage' do
-    it do
-      is_expected
+    it 'delegates to head_pipeline' do
+      expect(subject)
         .to delegate_method(:builds_with_coverage)
         .to(:head_pipeline)
         .with_prefix

spec/serializers/merge_request_poll_widget_entity_spec.rb

@@ -287,19 +287,14 @@ RSpec.describe MergeRequestPollWidgetEntity do
   end
 
   describe '#builds_with_coverage' do
-    let(:result) { subject[:builds_with_coverage] }
-    let(:builds) do
-      [
+    it 'serializes the builds with coverage' do
+      allow(resource).to receive(:head_pipeline_builds_with_coverage).and_return([
         double(name: 'rspec', coverage: 91.5),
         double(name: 'jest', coverage: 94.1)
-      ]
-    end
+      ])
 
-    before do
-      allow(resource).to receive(:head_pipeline_builds_with_coverage).and_return(builds)
-    end
+      result = subject[:builds_with_coverage]
 
-    it 'serializes the builds with coverage' do
       expect(result).to eq([
         { name: 'rspec', coverage: 91.5 },
         { name: 'jest', coverage: 94.1 }