Log unmatched mocks to the console for tests (#10502)

* Log a warning to the console when there are unmatched mocks in MockLink for a request.

* Silence expected warnings in other MockedProvider tests.

* Update docs to document the `silenceWarnings` option.

* Add a changeset

* Improve warning message displayed in console for unmatched mocks.

* Rename silenceWarnings to showWarnings

* Minor adjustment to changeset wording

* Fix default value reference in docs for showWarnings

* Fix broken test due to change in warnings shown to console for MockLink

.changeset/funny-files-suffer.md

@@ -0,0 +1,5 @@
+---
+'@apollo/client': patch
+---
+
+Log a warning to the console when a mock passed to `MockedProvider` or `MockLink` cannot be matched to a query during a test. This makes it easier to debug user errors in the mock setup, such as typos, especially if the query under test is using an `errorPolicy` set to `ignore`, which makes it difficult to know that a match did not occur.

docs/source/api/react/testing.md

@@ -119,6 +119,22 @@ Props to pass down to the `MockedProvider`'s child.
 </td>
 </tr>
 
+<tr>
+<td>
+
+###### `showWarnings`
+
+`boolean`
+</td>
+<td>
+
+When a request fails to match a mock, a warning is logged to the console to indicate the mismatch. Set this to `false` to silence these warnings.
+
+The default value is `true`.
+
+</td>
+</tr>
+
 </tbody>
 </table>
 

docs/source/development-testing/testing.mdx

@@ -394,12 +394,19 @@ In order to properly test local state using `MockedProvider`, you'll need to pas
 `MockedProvider` creates its own ApolloClient instance behind the scenes like this:
 
 ```jsx
-const { mocks, addTypename, defaultOptions, cache, resolvers, link } =
-  this.props;
+const { 
+  mocks,
+  addTypename,
+  defaultOptions,
+  cache,
+  resolvers,
+  link,
+  showWarnings,
+} = this.props;
 const client = new ApolloClient({
   cache: cache || new Cache({ addTypename }),
   defaultOptions,
-  link: link || new MockLink(mocks || [], addTypename),
+  link: link || new MockLink(mocks || [], addTypename, { showWarnings }),
   resolvers,
 });
 ```

src/core/__tests__/ObservableQuery.ts

@@ -15,7 +15,7 @@ import { ApolloLink } from '../../link/core';
 import { InMemoryCache, NormalizedCacheObject } from '../../cache';
 import { ApolloError } from '../../errors';
 
-import { itAsync, mockSingleLink, subscribeAndCount } from '../../testing';
+import { itAsync, MockLink, mockSingleLink, subscribeAndCount } from '../../testing';
 import mockQueryManager from '../../testing/core/mocking/mockQueryManager';
 import mockWatchQuery from '../../testing/core/mocking/mockWatchQuery';
 import wrap from '../../testing/core/wrap';
@@ -1509,11 +1509,25 @@ describe('ObservableQuery', () => {
           };
         }
 
-        const observableWithVarsVar: ObservableQuery<any> = mockWatchQuery(
-          reject,
-          makeMock("a", "b", "c"),
-          makeMock("d", "e"),
-        );
+        // We construct the queryManager manually here rather than using 
+        // `mockWatchQuery` because we need to silence console warnings for 
+        // unmatched variables since. This test checks for calls to 
+        // `console.warn` and unfortunately `mockSingleLink` (used by 
+        // `mockWatchQuery`) does not support the ability to disable warnings 
+        // without introducing a breaking change. Instead we construct this 
+        // manually to be able to turn off warnings for this test.
+        const mocks = [makeMock('a', 'b', 'c'), makeMock('d', 'e')];
+        const firstRequest = mocks[0].request;
+        const queryManager = new QueryManager({
+          cache: new InMemoryCache({ addTypename: false }),
+          link: new MockLink(mocks, true, { showWarnings: false })
+        })
+
+        const observableWithVarsVar = queryManager.watchQuery({
+          query: firstRequest.query,
+          variables: firstRequest.variables,
+          notifyOnNetworkStatusChange: false
+        });
 
         subscribeAndCount(error => {
           expect(error.message).toMatch(
@@ -1536,7 +1550,7 @@ describe('ObservableQuery', () => {
             // to call refetch(variables).
             observableWithVarsVar.refetch({
               variables: { vars: ["d", "e"] },
-            }).then(result => {
+            } as any).then(result => {
               reject(`unexpected result ${JSON.stringify(result)}; should have thrown`);
             }, error => {
               expect(error.message).toMatch(

src/testing/core/index.ts

@@ -2,6 +2,7 @@ export {
   MockLink,
   mockSingleLink,
   MockedResponse,
+  MockLinkOptions,
   ResultFunction
 } from './mocking/mockLink';
 export {

src/testing/core/mocking/mockLink.ts

@@ -29,6 +29,10 @@ export interface MockedResponse<TData = Record<string, any>> {
   newData?: ResultFunction<FetchResult>;
 }
 
+export interface MockLinkOptions {
+  showWarnings?: boolean;
+}
+
 function requestToKey(request: GraphQLRequest, addTypename: Boolean): string {
   const queryString =
     request.query &&
@@ -40,14 +44,18 @@ function requestToKey(request: GraphQLRequest, addTypename: Boolean): string {
 export class MockLink extends ApolloLink {
   public operation: Operation;
   public addTypename: Boolean = true;
+  public showWarnings: boolean = true;
   private mockedResponsesByKey: { [key: string]: MockedResponse[] } = {};
 
   constructor(
     mockedResponses: ReadonlyArray<MockedResponse>,
-    addTypename: Boolean = true
+    addTypename: Boolean = true,
+    options: MockLinkOptions = Object.create(null)
   ) {
     super();
     this.addTypename = addTypename;
+    this.showWarnings = options.showWarnings ?? true;
+
     if (mockedResponses) {
       mockedResponses.forEach(mockedResponse => {
         this.addMockedResponse(mockedResponse);
@@ -102,6 +110,14 @@ Failed to match ${unmatchedVars.length} mock${
 } for this query. The mocked response had the following variables:
 ${unmatchedVars.map(d => `  ${stringifyForDisplay(d)}`).join('\n')}
 ` : ""}`);
+
+      if (this.showWarnings) {
+        console.warn(
+          configError.message + 
+            '\nThis typically indicates a configuration error in your mocks ' +
+            'setup, usually due to a typo or mismatched variable.'
+        );
+      }
     } else {
       mockedResponses.splice(responseIndex, 1);
 

src/testing/react/MockedProvider.tsx

@@ -17,6 +17,7 @@ export interface MockedProviderProps<TSerializedCache = {}> {
   childProps?: object;
   children?: any;
   link?: ApolloLink;
+  showWarnings?: boolean;
 }
 
 export interface MockedProviderState {
@@ -40,14 +41,16 @@ export class MockedProvider extends React.Component<
       defaultOptions,
       cache,
       resolvers,
-      link
+      link,
+      showWarnings,
     } = this.props;
     const client = new ApolloClient({
       cache: cache || new Cache({ addTypename }),
       defaultOptions,
       link: link || new MockLink(
         mocks || [],
         addTypename,
+        { showWarnings }
       ),
       resolvers,
     });

src/testing/react/__tests__/MockedProvider.test.tsx

@@ -175,7 +175,7 @@ describe('General use', () => {
     };
 
     render(
-      <MockedProvider mocks={mocks}>
+      <MockedProvider showWarnings={false} mocks={mocks}>
         <Component {...variables2} />
       </MockedProvider>
     );
@@ -215,7 +215,7 @@ describe('General use', () => {
     };
 
     render(
-      <MockedProvider mocks={mocks2}>
+      <MockedProvider showWarnings={false} mocks={mocks2}>
         <Component {...variables2} />
       </MockedProvider>
     );
@@ -325,7 +325,7 @@ describe('General use', () => {
     ];
 
     render(
-      <MockedProvider mocks={mocksDifferentQuery}>
+      <MockedProvider showWarnings={false} mocks={mocksDifferentQuery}>
         <Component {...variables} />
       </MockedProvider>
     );
@@ -435,7 +435,10 @@ describe('General use', () => {
       return null;
     }
 
-    const link = ApolloLink.from([errorLink, new MockLink([])]);
+    const link = ApolloLink.from([
+      errorLink,
+      new MockLink([], true, { showWarnings: false })
+    ]);
 
     render(
       <MockedProvider link={link}>
@@ -485,14 +488,149 @@ describe('General use', () => {
     expect(errorThrown).toBeFalsy();
   });
 
+  it('shows a warning in the console when there is no matched mock', async () => {
+    const consoleSpy = jest.spyOn(console, 'warn').mockImplementation(() => {});
+    let finished = false;
+    function Component({ ...variables }: Variables) {
+      const { loading } = useQuery<Data, Variables>(query, { variables });
+      if (!loading) {
+        finished = true;
+      }
+      return null;
+    }
+
+    const mocksDifferentQuery = [
+      {
+        request: {
+          query: gql`
+            query OtherQuery {
+              otherQuery {
+                id
+              }
+            }
+          `,
+          variables
+        },
+        result: { data: { user } }
+      }
+    ];
+
+    render(
+      <MockedProvider mocks={mocksDifferentQuery}>
+        <Component {...variables} />
+      </MockedProvider>
+    );
+
+    await waitFor(() => {
+      expect(finished).toBe(true);
+    });
+
+    expect(console.warn).toHaveBeenCalledTimes(1);
+    expect(console.warn).toHaveBeenCalledWith(
+      expect.stringContaining('No more mocked responses for the query')
+    );
+
+    consoleSpy.mockRestore();
+  });
+
+  it('silences console warning for unmatched mocks when `showWarnings` is `false`', async () => {
+    const consoleSpy = jest.spyOn(console, 'warn');
+    let finished = false;
+    function Component({ ...variables }: Variables) {
+      const { loading } = useQuery<Data, Variables>(query, { variables });
+      if (!loading) {
+        finished = true;
+      }
+      return null;
+    }
+
+    const mocksDifferentQuery = [
+      {
+        request: {
+          query: gql`
+            query OtherQuery {
+              otherQuery {
+                id
+              }
+            }
+          `,
+          variables
+        },
+        result: { data: { user } }
+      }
+    ];
+
+    render(
+      <MockedProvider mocks={mocksDifferentQuery} showWarnings={false}>
+        <Component {...variables} />
+      </MockedProvider>
+    );
+
+    await waitFor(() => {
+      expect(finished).toBe(true);
+    });
+
+    expect(console.warn).not.toHaveBeenCalled();
+
+    consoleSpy.mockRestore();
+  });
+
+  it('silences console warning for unmatched mocks when passing `showWarnings` to `MockLink` directly', async () => {
+    const consoleSpy = jest.spyOn(console, 'warn');
+    let finished = false;
+    function Component({ ...variables }: Variables) {
+      const { loading } = useQuery<Data, Variables>(query, { variables });
+      if (!loading) {
+        finished = true;
+      }
+      return null;
+    }
+
+    const mocksDifferentQuery = [
+      {
+        request: {
+          query: gql`
+            query OtherQuery {
+              otherQuery {
+                id
+              }
+            }
+          `,
+         variables
+        },
+        result: { data: { user } }
+      }
+    ];
+
+    const link = new MockLink(
+      mocksDifferentQuery,
+      false,
+      { showWarnings: false }
+    );
+
+    render(
+      <MockedProvider link={link}>
+        <Component {...variables} />
+      </MockedProvider>
+    );
+
+    await waitFor(() => {
+      expect(finished).toBe(true);
+    });
+
+    expect(console.warn).not.toHaveBeenCalled();
+
+    consoleSpy.mockRestore();
+  });
+
   itAsync('should support custom error handling using setOnError', (resolve, reject) => {
     let finished = false;
     function Component({ ...variables }: Variables) {
       useQuery<Data, Variables>(query, { variables });
       return null;
     }
 
-    const mockLink = new MockLink([]);
+    const mockLink = new MockLink([], true, { showWarnings: false });
     mockLink.setOnError(error => {
       expect(error).toMatchSnapshot();
       finished = true;
@@ -521,7 +659,7 @@ describe('General use', () => {
       return null;
     }
 
-    const mockLink = new MockLink([]);
+    const mockLink = new MockLink([], true, { showWarnings: false });
     mockLink.setOnError(() => {
       throw new Error('oh no!');
     });