Add findAllByTestId Helper to Extended Wrappers

This allows you to find all instances by a `data-testid`, which is about
as handy as `findByTestId`. It is a shortcut to call `findAll` with a
given `data-testid` attribute.

spec/frontend/__helpers__/vue_test_utils_helper.js

@@ -45,9 +45,16 @@ export const extendedWrapper = (wrapper) => {
     return wrapper;
   }
 
-  return Object.defineProperty(wrapper, 'findByTestId', {
+  return Object.defineProperties(wrapper, {
+    findByTestId: {
       value(id) {
         return this.find(`[data-testid="${id}"]`);
       },
+    },
+    findAllByTestId: {
+      value(id) {
+        return this.findAll(`[data-testid="${id}"]`);
+      },
+    },
   });
 };

spec/frontend/__helpers__/vue_test_utils_helper_spec.js

@@ -88,5 +88,22 @@ describe('Vue test utils helpers', () => {
         expect(mockComponent.findByTestId(testId).exists()).toBe(true);
       });
     });
+
+    describe('findAllByTestId', () => {
+      const testId = 'a-component';
+      let mockComponent;
+
+      beforeEach(() => {
+        mockComponent = extendedWrapper(
+          shallowMount({
+            template: `<div><div data-testid="${testId}"></div><div data-testid="${testId}"></div></div>`,
+          }),
+        );
+      });
+
+      it('should find all components by test id', () => {
+        expect(mockComponent.findAllByTestId(testId)).toHaveLength(2);
+      });
+    });
   });
 });