Welcome to the final lesson of our course! Here, we'll learn how to test GraphQL APIs, ensuring that your server is robust and reliable. Testing is crucial for maintaining the stability and functionality of your API as it evolves.

Let's define a simple schema involving books. This schema includes the Book type, a Query for retrieving books, and a Mutation for adding a book.

Here's a brief explanation:

• Book: Represents a book with id, title, and author fields.
• Query books: Fetches a list of books.
• Mutation addBook: Adds a new book.

Let's implement the books query and see how to test it. We'll use a simple array to store our books.

In Apollo Server 4, testing is handled differently as it does not utilize apollo-server-testing. Instead, we can use tools like @apollo/server combined with graphql-testing utilities or direct request simulation.

Here's a basic approach to testing the books query using Apollo Server 4:

1. Set Up Apollo Server:

2. Write and Execute the Test Query:

When you run this code, it sets up the server and uses executeOperation to send the books query, receiving the results directly in your code for inspection. The expected output is:

Next, let's implement the addBook mutation and learn how to test it.

First, we define the resolver for the addBook mutation.

To test this mutation in Apollo Server 4, utilize the server's capabilities to execute operations:

1. Set Up Apollo Server and Execute the Mutation:

2. Write and Execute the Test Mutation:

When you run this code, the server executes the addBook mutation, and you should see the following output:

To sum up, in this lesson, you learned how to:

• Set up a basic GraphQL environment using Apollo Server 4.
• Define a simple GraphQL schema.
• Implement and test queries and mutations using Apollo Server's built-in operation execution methods.

These testing techniques ensure that your GraphQL API remains robust as it scales. Congratulations on completing the Comprehensive Intro to GraphQL in TypeScript course path! Now, you have a strong foundation in both creating and testing GraphQL APIs. Make sure to apply these skills in your future projects and dive deeper into more advanced topics as you grow your expertise. Happy coding!