Revert "DRY WorkPackageSchema#available_custom_fields spec"

This reverts commit 8e47f600b0.

spec/lib/api/v3/work_packages/schema/work_package_schema_spec.rb

@@ -99,20 +99,20 @@ describe ::API::V3::WorkPackages::Schema::WorkPackageSchema do
       let(:cf2) { double }
       let(:cf3) { double }
 
-      before do
-        allow_message_expectations_on_nil
+      it 'is expected to return custom fields available in project AND type' do
         allow(type).to receive_message_chain(:custom_fields, :to_a).and_return([cf1, cf2])
         allow(project).to receive_message_chain(:all_work_package_custom_fields, :to_a)
           .and_return([cf2, cf3])
-      end
 
-      it 'is expected to return custom fields available in project AND type' do
         expect(subject.available_custom_fields).to eql([cf2])
       end
 
       context 'type missing' do
         let(:type) { nil }
         it 'returns an empty list' do
+          allow(project).to receive_message_chain(:all_work_package_custom_fields, :to_a)
+            .and_return([cf2, cf3])
+
           expect(subject.available_custom_fields).to eql([])
         end
       end
@@ -120,6 +120,8 @@ describe ::API::V3::WorkPackages::Schema::WorkPackageSchema do
       context 'project missing' do
         let(:project) { nil }
         it 'returns an empty list' do
+          allow(type).to receive_message_chain(:custom_fields, :to_a).and_return([cf1, cf2])
+
           expect(subject.available_custom_fields).to eql([])
         end
       end