fixed failing tests because of passed `null`

added spec to check for `head` file

app/assets/javascripts/ide/components/repo_editor.vue

@@ -19,7 +19,7 @@ export default {
     },
   },
   computed: {
-    ...mapState(['rightPanelCollapsed', 'viewer', 'delayViewerUpdated']),
+    ...mapState(['rightPanelCollapsed', 'viewer', 'delayViewerUpdated', 'panelResizing']),
     ...mapGetters(['currentMergeRequest', 'getStagedFile']),
     shouldHideEditor() {
       return this.file && this.file.binary && !this.file.raw;

spec/javascripts/ide/components/repo_editor_spec.js

@@ -163,7 +163,7 @@ describe('RepoEditor', () => {
 
       vm.setupEditor();
 
-      expect(vm.editor.createModel).toHaveBeenCalledWith(vm.file);
+      expect(vm.editor.createModel).toHaveBeenCalledWith(vm.file, null);
       expect(vm.model).not.toBeNull();
     });
 
@@ -197,6 +197,20 @@ describe('RepoEditor', () => {
         done();
       });
     });
+
+    it('sets head model as staged file', () => {
+      spyOn(vm.editor, 'createModel').and.callThrough();
+
+      Editor.editorInstance.modelManager.dispose();
+
+      vm.$store.state.stagedFiles.push({ ...vm.file, key: 'staged' });
+      vm.file.staged = true;
+      vm.file.key = `unstaged-${vm.file.key}`;
+
+      vm.setupEditor();
+
+      expect(vm.editor.createModel).toHaveBeenCalledWith(vm.file, vm.$store.state.stagedFiles[0]);
+    });
   });
 
   describe('editor updateDimensions', () => {

spec/javascripts/ide/lib/common/model_spec.js

@@ -30,6 +30,19 @@ describe('Multi-file editor library model', () => {
     expect(model.baseModel).not.toBeNull();
   });
 
+  it('creates model with head file to compare against', () => {
+    const f = file('path');
+    model.dispose();
+
+    model = new Model(monaco, f, {
+      ...f,
+      content: '123 testing',
+    });
+
+    expect(model.head).not.toBeNull();
+    expect(model.getOriginalModel().getValue()).toBe('123 testing');
+  });
+
   it('adds eventHub listener', () => {
     expect(eventHub.$on).toHaveBeenCalledWith(
       `editor.update.model.dispose.${model.file.key}`,

spec/javascripts/ide/lib/editor_spec.js

@@ -88,7 +88,7 @@ describe('Multi-file editor library', () => {
 
       instance.createModel('FILE');
 
-      expect(instance.modelManager.addModel).toHaveBeenCalledWith('FILE');
+      expect(instance.modelManager.addModel).toHaveBeenCalledWith('FILE', null);
     });
   });