1 files changed, 80 insertions, 0 deletions
diff --git a/qa/qa/specs/features/browser_ui/3_create/merge_request/view_merge_request_merge_ref_diff_spec.rb b/qa/qa/specs/features/browser_ui/3_create/merge_request/view_merge_request_merge_ref_diff_spec.rb
new file mode 100644
index 00000000000..7844d0d7ccb
--- /dev/null
+++ b/qa/qa/specs/features/browser_ui/3_create/merge_request/view_merge_request_merge_ref_diff_spec.rb
@@ -0,0 +1,80 @@
+# frozen_string_literal: true
+
+module QA
+  RSpec.describe 'Create', :requires_admin do
+    describe 'View merge request merge-ref diff' do
+      let(:merge_request) do
+        Resource::MergeRequest.fabricate_via_api! do |merge_request|
+          merge_request.title = 'This is a merge request'
+          merge_request.description = '... for viewing merge-ref and merge-base diffs'
+          merge_request.file_content = 'This exists on the source branch only'
+        end
+      end
+
+      let(:new_file_name) { "added_file-#{SecureRandom.hex(8)}.txt" }
+
+      before do
+        commit_to_branch(merge_request.target_branch, new_file_name)
+        commit_to_branch(merge_request.source_branch, new_file_name)
+
+        Flow::Login.sign_in
+      end
+
+      context 'when the feature flag default_merge_ref_for_diffs is enabled' do
+        before do
+          Runtime::Feature.enable('default_merge_ref_for_diffs', project: merge_request.project)
+
+          merge_request.visit!
+        end
+
+        it 'views the merge-ref diff by default' do
+          Page::MergeRequest::Show.perform do |mr_page|
+            mr_page.click_diffs_tab
+            mr_page.click_target_version_dropdown
+
+            expect(mr_page.version_dropdown_content).to include('master (HEAD)')
+            expect(mr_page.version_dropdown_content).not_to include('master (base)')
+            expect(mr_page).to have_file(merge_request.file_name)
+            expect(mr_page).not_to have_file(new_file_name)
+          end
+        end
+      end
+
+      context 'when the feature flag default_merge_ref_for_diffs is disabled' do
+        before do
+          Runtime::Feature.disable('default_merge_ref_for_diffs', project: merge_request.project)
+
+          merge_request.visit!
+        end
+
+        it 'views the merge-base diff by default' do
+          Page::MergeRequest::Show.perform do |mr_page|
+            mr_page.click_diffs_tab
+            mr_page.click_target_version_dropdown
+
+            expect(mr_page.version_dropdown_content).to include('master (HEAD)')
+            expect(mr_page.version_dropdown_content).to include('master (base)')
+            expect(mr_page).to have_file(merge_request.file_name)
+            expect(mr_page).to have_file(new_file_name)
+          end
+        end
+      end
+
+      def commit_to_branch(branch, file)
+        Resource::Repository::Commit.fabricate_via_api! do |commit|
+          commit.project = merge_request.project
+          commit.branch = branch
+          commit.commit_message = "Add new file on #{branch}"
+          commit.add_files(
+            [
+                {
+                    file_path: file,
+                    content: "This exists on source and target branches"
+                }
+            ]
+          )
+        end
+      end
+    end
+  end
+end