Unit testing for GraphQL resolvers

Unit testing GraphQL resolvers in NestJS is about verifying that each resolver behaves as expected, independent of the others. In a code-first approach, where the schema is generated based on TypeScript decorators, testing becomes crucial to ensure that the schema accurately represents the underlying business logic encapsulated within these resolvers.

For our demonstration, we’ll be extending the user management system developed in Chapter 6, focusing on the resolvers within our code-first GraphQL API. This approach allows us to validate the logic of fetching, creating, updating, and deleting users, ensuring that our GraphQL API is robust and behaves predictably under various conditions.

Setting up for testing

Before we dive into writing tests, let’s set up our testing environment. Assuming you’ve followed along from Chapter 6, you should have a user management system with resolvers ready for testing. If not, I encourage...