Add table for merge request commits

This is an ID-less table with just three columns: an association to the merge
request diff the commit belongs to, the relative order of the commit within the
merge request diff, and the commit SHA itself.

Previously we stored much more information about the commits, so that we could
display them even when they were deleted from the repo. Since 8.0, we ensure
that those commits are kept around for as long as the target repo itself is, so
we don't need to duplicate that data in the database.

1 files changed, 3 insertions, 3 deletions

diff --git a/spec/models/merge_request_diff_spec.rb b/spec/models/merge_request_diff_spec.rb
index 4ad4abaa572..edc2f4bb9f0 100644
--- a/spec/models/merge_request_diff_spec.rb
+++ b/spec/models/merge_request_diff_spec.rb
@@ -98,7 +98,7 @@ describe MergeRequestDiff, models: true do
     end
 
     it 'saves empty state' do
-      allow_any_instance_of(MergeRequestDiff).to receive(:commits)
+      allow_any_instance_of(MergeRequestDiff).to receive_message_chain(:compare, :commits)
         .and_return([])
 
       mr_diff = create(:merge_request).merge_request_diff
@@ -107,14 +107,14 @@ describe MergeRequestDiff, models: true do
     end
   end
 
-  describe '#commits_sha' do
+  describe '#commit_shas' do
     it 'returns all commits SHA using serialized commits' do
       subject.st_commits = [
         { id: 'sha1' },
         { id: 'sha2' }
       ]
 
-      expect(subject.commits_sha).to eq(%w(sha1 sha2))
+      expect(subject.commit_shas).to eq(%w(sha1 sha2))
     end
   end