1 files changed, 61 insertions, 0 deletions
diff --git a/spec/services/merge_requests/reload_merge_head_diff_service_spec.rb b/spec/services/merge_requests/reload_merge_head_diff_service_spec.rb
new file mode 100644
index 00000000000..3152a4e3861
--- /dev/null
+++ b/spec/services/merge_requests/reload_merge_head_diff_service_spec.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe MergeRequests::ReloadMergeHeadDiffService do
+  let(:merge_request) { create(:merge_request) }
+
+  subject { described_class.new(merge_request).execute }
+
+  describe '#execute' do
+    before do
+      MergeRequests::MergeToRefService
+        .new(merge_request.project, merge_request.author)
+        .execute(merge_request)
+    end
+
+    it 'creates a merge head diff' do
+      expect(subject[:status]).to eq(:success)
+      expect(merge_request.reload.merge_head_diff).to be_present
+    end
+
+    context 'when merge ref head is not present' do
+      before do
+        allow(merge_request).to receive(:merge_ref_head).and_return(nil)
+      end
+
+      it 'returns error' do
+        expect(subject[:status]).to eq(:error)
+      end
+    end
+
+    context 'when failed to create merge head diff' do
+      before do
+        allow(merge_request).to receive(:create_merge_head_diff!).and_raise('fail')
+      end
+
+      it 'returns error' do
+        expect(subject[:status]).to eq(:error)
+      end
+    end
+
+    context 'when there is existing merge head diff' do
+      let!(:existing_merge_head_diff) { create(:merge_request_diff, :merge_head, merge_request: merge_request) }
+
+      it 'recreates merge head diff' do
+        expect(subject[:status]).to eq(:success)
+        expect(merge_request.reload.merge_head_diff).not_to eq(existing_merge_head_diff)
+      end
+    end
+
+    context 'when default_merge_ref_for_diffs feature flag is disabled' do
+      before do
+        stub_feature_flags(default_merge_ref_for_diffs: false)
+      end
+
+      it 'returns error' do
+        expect(subject[:status]).to eq(:error)
+      end
+    end
+  end
+end