Resolver unit tests in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this resolver unit test?

Given a GraphQL resolver that returns a list of users, what will be the result of this unit test?

const users = [{id: 1, name: "Alice"}, {id: 2, name: "Bob"}];

const resolver = {
  Query: {
    users: () => users
  }
};

// Test
const result = resolver.Query.users();
console.log(result.length);

GraphQL

const users = [{id: 1, name: "Alice"}, {id: 2, name: "Bob"}];

const resolver = {
  Query: {
    users: () => users
  }
};

const result = resolver.Query.users();
console.log(result.length);

A 0

B undefined

C 2

D 1

💡 Hint

Think about how many user objects are in the array returned by the resolver.

The resolver returns the array of users with two objects, so the length is 2.

📝 Syntax

intermediate

Which option causes a syntax error in this resolver test?

Identify which resolver unit test code snippet will cause a syntax error.

const resolver = {
  Query: {
    user: (parent, args) => {
      return {id: args.id, name: "Test User"};
    }
  }
};

// Test call
const result = resolver.Query.user(null, {id: 1});
console.log(result);

GraphQL

const resolver = {
  Query: {
    user: (parent, args) => {
      return {id: args.id, name: "Test User"};
    }
  }
};

const result = resolver.Query.user(null, {id: 1});
console.log(result);

A const result = resolver.Query.user(null, id: 1); console.log(result);

B const result = resolver.Query.user(null, {id: 1}); console.log(result);

C ;)tluser(gol.elosnoc ;)}1 :di{ ,llun(resu.yreuQ.revloser = tluser tsnoc

D onst result = resolver.Query.user(null, {id: 1}); console.log(result);

💡 Hint

Look carefully at how the arguments are passed to the resolver function.

Option A passes arguments incorrectly without braces around the object, causing a syntax error.

❓ optimization

advanced

Which option optimizes resolver unit test performance best?

You want to optimize a resolver unit test that fetches user data from a mock database. Which approach reduces test runtime most effectively?

A Use a mock function that returns a static user object immediately.

B Call the real database in each test to ensure data accuracy.

C Use a delayed promise to simulate network latency in tests.

D Run tests sequentially with real database calls.

💡 Hint

Think about what makes tests fast and reliable.

Using a mock function returning static data avoids delays and external dependencies, speeding up tests.

🔧 Debug

advanced

Why does this resolver unit test fail?

Consider this resolver and test code:

const resolver = {
  Query: {
    user: (parent, args) => {
      if (!args.id) throw new Error("ID required");
      return {id: args.id, name: "User" + args.id};
    }
  }
};

// Test
try {
  resolver.Query.user(null, {});
} catch (e) {
  console.log(e.message);
}

What is the output of the test?

A TypeError

B undefined

C "Userundefined"

D "ID required"

💡 Hint

Check what happens when args.id is missing.

The resolver throws an error if args.id is missing, so the catch block logs "ID required".

🧠 Conceptual

expert

What is the main benefit of mocking dependencies in resolver unit tests?

Why do developers mock external services or databases when writing resolver unit tests?

A To ensure the resolver always connects to the real database.

B To isolate the resolver logic and test it without external side effects.

C To slow down tests and simulate real network delays.

D To increase the complexity of tests by adding more dependencies.

💡 Hint

Think about what makes unit tests reliable and fast.

Mocking isolates the resolver so tests focus only on its logic, avoiding unpredictable external factors.