Resolver unit tests in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a resolver in GraphQL?

A resolver is a function that fetches the data for a specific field in a GraphQL query. It tells the server how to get the data requested by the client.

beginner

Why do we write unit tests for resolvers?

Unit tests for resolvers check that each resolver returns the correct data and handles errors properly. This helps catch bugs early and ensures the API works as expected.

intermediate

What is a common tool used to mock data sources in resolver unit tests?

A common tool is Jest with mocking functions. It lets you simulate database calls or API responses so you can test resolvers without real data sources.

intermediate

How do you test error handling in a resolver?

You simulate an error in the data source or input and check if the resolver returns the correct error message or throws an error as expected.

advanced

What is the difference between unit testing a resolver and integration testing a GraphQL API?

Unit testing a resolver focuses on one resolver function in isolation, often mocking data sources. Integration testing checks how multiple parts work together, including the full GraphQL query execution.

What does a resolver function do in GraphQL?

A Validates client queries

B Defines the GraphQL schema

C Runs the GraphQL server

D Fetches data for a specific field

Resolvers fetch the data for each field requested in a GraphQL query.

Which tool is commonly used to mock data in resolver unit tests?

A Jest

B React

C Express

D MongoDB

Jest is a popular testing framework that supports mocking functions for unit tests.

What should you test in a resolver unit test?

A Network latency

B User interface layout

C Correct data return and error handling

D Database schema design

Unit tests check if the resolver returns correct data and handles errors properly.

How do you isolate a resolver for unit testing?

A Mock external data sources

B Run the full server

C Use real database connections

D Test the entire API

Mocking data sources isolates the resolver so you test only its logic.

What is the main difference between unit and integration tests for GraphQL?

A Unit tests check UI; integration tests check backend

B Unit tests check one resolver; integration tests check multiple parts working together

C Unit tests run slower than integration tests

D Unit tests require a database; integration tests do not

Unit tests focus on single resolvers; integration tests cover the full query execution flow.

Explain how you would write a unit test for a GraphQL resolver that fetches user data.

Think about isolating the resolver and simulating data.

Describe the benefits of unit testing resolvers in a GraphQL API.

Consider how testing helps in development and maintenance.