Fix attr reader to force the intended values for source and target shas

app/models/merge_request.rb

@@ -238,10 +238,14 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def target_branch_sha
+    return @target_branch_sha if defined?(@target_branch_sha)
+
     target_branch_head.try(:sha)
   end
 
   def source_branch_sha
+    return @source_branch_sha if defined?(@source_branch_sha)
+
     source_branch_head.try(:sha)
   end
 

spec/models/merge_request_spec.rb

@@ -65,11 +65,11 @@ describe MergeRequest, models: true do
   end
 
   describe '#target_branch_sha' do
-    context 'when the target branch does not exist anymore' do
-      let(:project) { create(:project) }
+    let(:project) { create(:project) }
 
-      subject { create(:merge_request, source_project: project, target_project: project) }
+    subject { create(:merge_request, source_project: project, target_project: project) }
 
+    context 'when the target branch does not exist' do
       before do
         project.repository.raw_repository.delete_branch(subject.target_branch)
       end
@@ -78,6 +78,12 @@ describe MergeRequest, models: true do
         expect(subject.target_branch_sha).to be_nil
       end
     end
+
+    it 'returns memoized value' do
+      subject.target_branch_sha = '8ffb3c15a5475e59ae909384297fede4badcb4c7'
+
+      expect(subject.target_branch_sha).to eq '8ffb3c15a5475e59ae909384297fede4badcb4c7'
+    end
   end
 
   describe '#source_branch_sha' do
@@ -103,6 +109,12 @@ describe MergeRequest, models: true do
         expect(subject.source_branch_sha).to be_nil
       end
     end
+
+    it 'returns memoized value' do
+      subject.source_branch_sha = '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b'
+
+      expect(subject.source_branch_sha).to eq '2e5d3239642f9161dcbbc4b70a211a68e5e45e2b'
+    end
   end
 
   describe '#to_reference' do