Improve GraphQL tests that use nil checks

spec/graphql/types/admin/analytics/usage_trends/measurement_type_spec.rb

@@ -36,8 +36,14 @@ RSpec.describe GitlabSchema.types['UsageTrendsMeasurement'] do
     end
 
     context 'when the user is not admin' do
-      it 'returns no data' do
-        expect(subject.dig('data', 'usageTrendsMeasurements')).to be_nil
+      it 'returns an error' do
+        expected_err = "The resource that you are attempting to access does not exist or you don't have permission to perform this action"
+
+        expect(subject["errors"].first["message"]).to eq(expected_err)
+      end
+
+      it 'does not return usageTrendsMeasurements data' do
+        expect(subject["data"]["usageTrendsMeasurements"]).to be_nil
       end
     end
 
@@ -48,7 +54,7 @@ RSpec.describe GitlabSchema.types['UsageTrendsMeasurement'] do
         stub_application_setting(admin_mode: false)
       end
 
-      it 'returns data' do
+      it 'returns usageTrendsMeasurements data' do
         expect(subject.dig('data', 'usageTrendsMeasurements', 'nodes')).not_to be_empty
       end
     end

spec/graphql/types/ci/job_token_scope_type_spec.rb

@@ -12,7 +12,7 @@ RSpec.describe GitlabSchema.types['CiJobTokenScopeType'] do
   end
 
   describe 'query' do
-    let_it_be(:project) { create(:project, ci_job_token_scope_enabled: true).tap(&:save!) }
+    let(:project) { create(:project, ci_job_token_scope_enabled: true).tap(&:save!) }
     let_it_be(:current_user) { create(:user) }
 
     let(:query) do
@@ -65,8 +65,12 @@ RSpec.describe GitlabSchema.types['CiJobTokenScopeType'] do
             project.ci_cd_settings.update!(job_token_scope_enabled: false)
           end
 
+          it 'does not return an error' do
+            expect(subject['errors']).to be_nil
+          end
+
           it 'returns nil' do
-            expect(subject.dig('data', 'project', 'ciJobTokenScope')).to be_nil
+            expect(subject['data']['project']['ciJobTokenScope']).to be_nil
           end
         end
       end

spec/graphql/types/issue_type_spec.rb

@@ -66,10 +66,16 @@ RSpec.describe GitlabSchema.types['Issue'] do
     end
 
     context 'when user does not have the permission' do
-      it 'returns no data' do
+      before do
         allow(Ability).to receive(:allowed?).with(user, :read_project, project).and_return(false)
+      end
 
-        expect(subject.dig(:data, :project)).to eq(nil)
+      it 'does not return an error' do
+        expect(subject['errors']).to be_nil
+      end
+
+      it 'returns no data' do
+        expect(subject['data']['project']).to be_nil
       end
     end