Bug(mock): Resolver with return type List is not use value from mock resolver.

[IttisutBm]

// server.js
const server = new ApolloServer({
  ...
  mockEntireSchema: false,
});

// schema.gql
type User {
   id: ObjectId
   username: String
   nickname: String
}

// mocks.js
export default {
    User(){
       nickname: 'John'
    }
   String: ()=>'Bob'
}

// resolvers.js
export default {
    Query: {
        // Both of query get Object type User with `undefined` value on `nickname` prop
        // `user resolver` is working correctly. it return user with nickname `John`
        user:(root, {id}, { db })=>db.get('user').find({ id }).value() 
        // `users resolver` is wrong. it return user with nickname `Bob`
        users:(root, args, { db })=>db.get('user').value()  
}

I found that we can fix this by edit this function:

graphql-tools/packages/mock/src/addMocksToSchema.ts

Lines 180 to 206 in b8308ef

	newFieldConfig.resolve = async (rootObject, args, context, info) => {
	const [mockedValue, resolvedValue] = await Promise.all([
	mockResolver(rootObject, args, context, info),
	oldResolver(rootObject, args, context, info),
	]);
	// In case we couldn't mock
	if (mockedValue instanceof Error) {
	// only if value was not resolved, populate the error.
	if (undefined === resolvedValue) {
	throw mockedValue;
	}
	return resolvedValue;
	}
	if (resolvedValue instanceof Date && mockedValue instanceof Date) {
	return undefined !== resolvedValue ? resolvedValue : mockedValue;
	}
	if (isObject(mockedValue) && isObject(resolvedValue)) {
	// Object.assign() won't do here, as we need to all properties, including
	// the non-enumerable ones and defined using Object.defineProperty
	const emptyObject = Object.create(Object.getPrototypeOf(resolvedValue));
	return copyOwnProps(emptyObject, resolvedValue, mockedValue);
	}
	return undefined !== resolvedValue ? resolvedValue : mockedValue;
	};

In case of return type List, it will go to this line.

graphql-tools/packages/mock/src/addMocksToSchema.ts

Line 205 in b8308ef

return undefined !== resolvedValue ? resolvedValue : mockedValue;

This mean it will return list value from resolver and ignore list value from mock resolver which is wrong.
We need to merge value from resolver and mock server together and it done.
I add this code above that line and it work!.

if(Array.isArray(mockedValue) && Array.isArray(resolvedValue)){
    const results = []
    resolvedValue.forEach(function(element,index,array) {
        const emptyObject = Object.create(Object.getPrototypeOf(resolvedValue[index]));
        results.push(copyOwnProps(emptyObject, resolvedValue[index], mockedValue[index]))
    })
    return results;
}

I'm not quite sure. this is the right approach or not.
Hope it help. 😄