feat(mergeMocks): support Promises (#1883)

packages/mock/src/mocking.ts

@@ -336,6 +336,9 @@ function mergeMocks(genericMockFunction: () => any, customMock: any): any {
   if (Array.isArray(customMock)) {
     return customMock.map((el: any) => mergeMocks(genericMockFunction, el));
   }
+  if (customMock instanceof Promise) {
+    return customMock.then((res: any) => mergeObjects(genericMockFunction(), res));
+  }
   if (isObject(customMock)) {
     return mergeObjects(genericMockFunction(), customMock);
   }

packages/mock/tests/mocking.spec.ts

@@ -1571,6 +1571,51 @@ describe('Mock', () => {
     expect(typeof result.data?.reviews[0]?.user?.first_name).toBe('string');
   });
 
+  it('should merge resolved result of a promise with default mock if available', async () => {
+    const resolvedName = 'Resolved name';
+    const mockedSecondName = 'mocked second name';
+    const mocks = {
+      MyType: () => ({
+        name: 'mocked name',
+        secondName: mockedSecondName,
+      }),
+      Query: () => ({
+        pendingQuery: () => Promise.resolve({
+          name: 'Resolved name'
+        }),
+      }),
+    };
+
+    let schema = buildSchema(/* GraphQL */ `
+      type MyType {
+        name: String
+        secondName: String
+      }
+      type Query {
+        pendingQuery: MyType
+      }
+    `);
+
+    schema = addMocksToSchema({ schema, mocks });
+
+    const result = await graphql({
+      schema,
+      source: /* GraphQL */ `
+        {
+          pendingQuery {
+            name
+            secondName
+          }
+        }
+      `,
+    });
+
+    expect(result.data?.pendingQuery).toEqual({
+      name: resolvedName,
+      secondName: mockedSecondName,
+    });
+  });
+
   // TODO add a test that checks that even when merging defaults, lists invoke
   // the function for every object, not just once per list.