Fixed diff files not expanding

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/54868

app/assets/javascripts/diffs/store/actions.js

@@ -148,7 +148,7 @@ export const scrollToLineIfNeededParallel = (_, line) => {
 };
 
 export const loadCollapsedDiff = ({ commit }, file) =>
-  axios.get(file.loadCollapsedDiffUrl).then(res => {
+  axios.get(file.load_collapsed_diff_url).then(res => {
     commit(types.ADD_COLLAPSED_DIFFS, {
       file,
       data: res.data,

spec/features/merge_request/user_expands_diff_spec.rb

@@ -0,0 +1,23 @@
+require 'spec_helper'
+
+describe 'User expands diff', :js do
+  let(:project) { create(:project, :public, :repository) }
+  let(:merge_request) { create(:merge_request, source_project: project, target_project: project) }
+
+  before do
+    visit(diffs_project_merge_request_path(project, merge_request))
+
+    wait_for_requests
+  end
+
+  it 'allows user to expand diff' do
+    page.within find('[id="19763941ab80e8c09871c0a425f0560d9053bcb3"]') do
+      click_link 'Click to expand it.'
+
+      wait_for_requests
+
+      expect(page).not_to have_content('Click to expand it.')
+      expect(page).to have_selector('.code')
+    end
+  end
+end

spec/javascripts/diffs/store/actions_spec.js

@@ -379,7 +379,7 @@ describe('DiffsStoreActions', () => {
 
   describe('loadCollapsedDiff', () => {
     it('should fetch data and call mutation with response and the give parameter', done => {
-      const file = { hash: 123, loadCollapsedDiffUrl: '/load/collapsed/diff/url' };
+      const file = { hash: 123, load_collapsed_diff_url: '/load/collapsed/diff/url' };
       const data = { hash: 123, parallelDiffLines: [{ lineCode: 1 }] };
       const mock = new MockAdapter(axios);
       mock.onGet(file.loadCollapsedDiffUrl).reply(200, data);