Test(DevOps Adoption): `groups` local resolver

Improve the tests for the `groups` local resolver
in the Admin/DevOps Adoption tab.

This should serve as a good example to how to test
local resolvers for GraphQL going forward

doc/development/fe_guide/graphql.md

@@ -833,7 +833,7 @@ If your application contains `@client` queries, most probably you will have an A
 ```javascript
 import createMockApollo from 'jest/helpers/mock_apollo_helper';
 ...
-fakeApollo = createMockApollo(requestHandlers, {});
+mockApollo = createMockApollo(requestHandlers, resolvers);
 ```
 
 Sometimes we want to test a `result` hook of the local query. In order to have it triggered, we need to populate a cache with correct data to be fetched with this query:
@@ -849,14 +849,14 @@ query fetchLocalUser {
 ```javascript
 import fetchLocalUserQuery from '~/design_management/graphql/queries/fetch_local_user.query.graphql';
 
-function createComponentWithApollo() {
+function createMockApolloProvider() {
   const requestHandlers = [
     [getDesignListQuery, jest.fn().mockResolvedValue(designListQueryResponse)],
     [permissionsQuery, jest.fn().mockResolvedValue(permissionsQueryResponse)],
   ];
 
-  fakeApollo = createMockApollo(requestHandlers, {});
-  fakeApollo.clients.defaultClient.cache.writeQuery({
+  mockApollo = createMockApollo(requestHandlers, {});
+  mockApollo.clients.defaultClient.cache.writeQuery({
     query: fetchLocalUserQuery,
     data: {
       fetchLocalUser: {
@@ -864,15 +864,107 @@ function createComponentWithApollo() {
         name: 'Test',
       },
     },
-  })
+  });
 
-  wrapper = shallowMount(Index, {
+  return mockApollo;
+}
+
+function createComponent(options = {}) {
+  const { mockApollo } = options;
+
+  return shallowMount(Index, {
     localVue,
-    apolloProvider: fakeApollo,
+    apolloProvider: mockApollo,
   });
 }
 ```
 
+Sometimes it is necessary to control what the local resolver returns and inspect how it is called by the component. This can be done by mocking your local resolver:
+
+```javascript
+import fetchLocalUserQuery from '~/design_management/graphql/queries/fetch_local_user.query.graphql';
+
+function createMockApolloProvider(options = {}) {
+  const { fetchLocalUserSpy } = options;
+
+  mockApollo = createMockApollo([], {
+    Query: {
+      fetchLocalUser: fetchLocalUserSpy,
+    },
+  });
+
+  // Necessary for local resolvers to be activated
+  mockApollo.clients.defaultClient.cache.writeQuery({
+    query: fetchLocalUserQuery,
+    data: {},
+  });
+
+  return mockApollo;
+}
+```
+
+In the test you can then control what the spy is supposed to do and inspect the component after the request have returned:
+
+```javascript
+describe('My Index test with `createMockApollo`', () => {
+  let wrapper;
+  let fetchLocalUserSpy;
+
+  afterEach(() => {
+    wrapper.destroy();
+    wrapper = null;
+    fetchLocalUserSpy = null;
+  });
+
+  describe('when loading', () => {
+    beforeEach(() => {
+      const mockApollo = createMockApolloProvider();
+      wrapper = createComponent({ mockApollo });
+    });
+
+    it('displays the loader', () => {
+      // Assess that the loader is present
+    });
+  });
+
+  describe('with data', () => {
+    beforeEach(async () => {
+      fetchLocalUserSpy = jest.fn().mockResolvedValue(localUserQueryResponse);
+      const mockApollo = createMockApolloProvider(fetchLocalUserSpy);
+      wrapper = createComponent({ mockApollo });
+      await waitForPromises();
+    });
+
+    it('should fetch data once', () => {
+      expect(fetchLocalUserSpy).toHaveBeenCalledTimes(1);
+    });
+
+    it('displays data', () => {
+      // Assess that data is present
+    });
+  });
+
+  describe('with error', () => {
+    const error = 'Error!';
+
+    beforeEach(async () => {
+      fetchLocalUserSpy = jest.fn().mockRejectedValueOnce(error);
+      const mockApollo = createMockApolloProvider(fetchLocalUserSpy);
+      wrapper = createComponent({ mockApollo });
+      await waitForPromises();
+    });
+
+    it('should fetch data once', () => {
+      expect(fetchLocalUserSpy).toHaveBeenCalledTimes(1);
+    });
+
+    it('displays the error', () => {
+      // Assess that the error is displayed
+    });
+  });
+});
+```
+
 ## Handling errors
 
 GitLab's GraphQL mutations currently have two distinct error modes: [Top-level](#top-level-errors) and [errors-as-data](#errors-as-data).

ee/app/assets/javascripts/admin/dev_ops_report/components/devops_adoption_app.vue

@@ -3,7 +3,7 @@ import { GlAlert, GlLoadingIcon } from '@gitlab/ui';
 import * as Sentry from '~/sentry/wrapper';
 import getGroupsQuery from '../graphql/queries/get_groups.query.graphql';
 import DevopsAdoptionEmptyState from './devops_adoption_empty_state.vue';
-import { DEVOPS_ADOPTION_STRINGS } from '../constants';
+import { DEVOPS_ADOPTION_STRINGS, MAX_REQUEST_COUNT } from '../constants';
 
 export default {
   name: 'DevopsAdoptionApp',
@@ -17,6 +17,7 @@ export default {
   },
   data() {
     return {
+      requestCount: MAX_REQUEST_COUNT,
       loadingError: false,
     };
   },
@@ -25,7 +26,9 @@ export default {
       query: getGroupsQuery,
       loadingKey: 'loading',
       result() {
-        if (this.groups?.pageInfo?.nextPage) {
+        this.requestCount -= 1;
+
+        if (this.requestCount > 0 && this.groups?.pageInfo?.nextPage) {
           this.fetchNextPage();
         }
       },
@@ -55,7 +58,8 @@ export default {
           },
           updateQuery: (previousResult, { fetchMoreResult }) => {
             const { nodes, ...rest } = fetchMoreResult.groups;
-            const previousNodes = previousResult.groups.nodes;
+            const { nodes: previousNodes } = previousResult.groups;
+
             return { groups: { ...rest, nodes: [...previousNodes, ...nodes] } };
           },
         })
@@ -65,9 +69,9 @@ export default {
 };
 </script>
 <template>
-  <gl-loading-icon v-if="isLoading" size="md" class="gl-my-5" />
-  <gl-alert v-else-if="loadingError" variant="danger" :dismissible="false" class="gl-mt-3">
+  <gl-alert v-if="loadingError" variant="danger" :dismissible="false" class="gl-mt-3">
     {{ $options.i18n.groupsError }}
   </gl-alert>
+  <gl-loading-icon v-else-if="isLoading" size="md" class="gl-my-5" />
   <devops-adoption-empty-state v-else-if="isEmpty" />
 </template>

ee/app/assets/javascripts/admin/dev_ops_report/constants.js

 import { s__ } from '~/locale';
 
+export const MAX_REQUEST_COUNT = 10;
 export const DEVOPS_ADOPTION_STRINGS = {
   app: {
     groupsError: s__('DevopsAdoption|There was an error fetching Groups'),

ee/spec/frontend/admin/dev_ops_report/mock_data.js

@@ -17,6 +17,12 @@ export const groupNodes = [
   },
 ];
 
+export const nextGroupNode = {
+  __typename: 'Group',
+  full_name: 'Baz',
+  id: 'baz',
+};
+
 export const groupPageInfo = {
   nextPage: 2,
 };