Added spec for context_commits_diff model and entity

app/models/context_commits_diff.rb

@@ -32,8 +32,8 @@ class ContextCommitsDiff
 
   def diff_refs
     Gitlab::Diff::DiffRefs.new(
-      base_sha: commits.last.diff_refs.base_sha,
-      head_sha: commits.first.diff_refs.head_sha
+      base_sha: commits.last&.diff_refs&.base_sha,
+      head_sha: commits.first&.diff_refs&.head_sha
     )
   end
 

spec/models/context_commits_diff_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe ContextCommitsDiff do
+  let(:merge_request_context_commit_diff_file) { create(:merge_request_context_commit_diff_file) }
+  let(:merge_request) { merge_request_context_commit_diff_file.merge_request_context_commit.merge_request }
+  let(:context_commits_diff) { merge_request.context_commits_diff }
+
+  subject { context_commits_diff }
+
+  describe '.commits_count' do
+    it 'reports commits count' do
+      expect(subject.commits_count).to be(1)
+    end
+  end
+
+  describe '.raw_diffs' do
+    it 'returns instance of Gitlab::Git::DiffCollection' do
+      expect(subject.raw_diffs).to be_a(Gitlab::Git::DiffCollection)
+    end
+  end
+end

spec/serializers/context_commits_diff_entity_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe ContextCommitsDiffEntity do
+  let(:merge_request_context_commit_diff_file) { create(:merge_request_context_commit_diff_file) }
+  let(:merge_request) { merge_request_context_commit_diff_file.merge_request_context_commit.merge_request }
+  let(:context_commits_diff) { merge_request.context_commits_diff }
+
+  context 'as json' do
+    describe '.diff_files' do
+      it 'returns diff files metadata' do
+        payload = ContextCommitsDiffEntity.represent(context_commits_diff).as_json
+
+        expect(payload[:commits_count]).to eq(1)
+      end
+    end
+  end
+end