GraphQL has gained popularity among developers due to its flexibility and efficiency when it comes to fetching data from APIs. When working with GraphQL, it is crucial to test queries and mutations to ensure the accuracy and reliability of the data being fetched or modified. In this blog post, we will explore how to effectively test GraphQL queries and mutations using JavaScript.

Setting Up the Testing Environment

To begin with, we need to set up our testing environment. The following are the steps involved in getting started with testing GraphQL queries and mutations:

1. Install Dependencies: Install the necessary testing libraries for GraphQL like graphql, graphql-tag, and a testing framework like Jest or Mocha.

2. Create a Testing File: Create a testing file where you will write your test cases. This file can have the .test.js extension.

3. Import Dependencies: Import the necessary dependencies such as the GraphQL client and the schema definition from your application.

4. Initialize the Client: Create an instance of the GraphQL client using the imported schema definition.

Testing GraphQL Queries

To test a GraphQL query, follow these steps:

1. Write Query Test Case: In your testing file, write a test case for the query. This involves defining the query in GraphQL syntax and passing it to the client for execution.

2. Execute the Query: Use the client to execute the query and retrieve the result.

3. Perform Assertions: Validate the result by asserting against expected data or specific properties of the response. You can use assertions provided by your testing framework or custom assertions.

4. Run the Test: Run the test using the testing framework. If all assertions pass, the test will succeed.

Here’s an example of a test case for a GraphQL query using Jest:

const { graphql } = require('graphql');
const { makeExecutableSchema } = require('graphql-tools');
const { typeDefs, resolvers } = require('./schema');

const schema = makeExecutableSchema({ typeDefs, resolvers });

test('Fetch User By ID', async () => {
  const query = `
    query {
      user(id: "123") {
        id
        name
        email
      }
    }
  `;

  const result = await graphql(schema, query);

  expect(result.data.user).toBeDefined();
  expect(result.data.user.id).toBe('123');
  expect(result.data.user.name).toBe('John Doe');
  expect(result.data.user.email).toBe('john.doe@example.com');
});

Testing GraphQL Mutations

To test a GraphQL mutation, follow these steps:

1. Write Mutation Test Case: In your testing file, write a test case for the mutation. Define the mutation in GraphQL syntax and pass it to the client for execution.

2. Execute the Mutation: Use the client to execute the mutation and retrieve the result.

3. Perform Assertions: Validate the result by asserting against expected data or specific properties of the response.

4. Run the Test: Run the test using the testing framework. If all assertions pass, the test will succeed.

Here’s an example of a test case for a GraphQL mutation using Jest:

const { graphql } = require('graphql');
const { makeExecutableSchema } = require('graphql-tools');
const { typeDefs, resolvers } = require('./schema');

const schema = makeExecutableSchema({ typeDefs, resolvers });

test('Create New User', async () => {
  const mutation = `
    mutation {
      createUser(input: {
        name: "Jane Doe",
        email: "jane.doe@example.com"
      }) {
        id
        name
        email
      }
    }
  `;

  const result = await graphql(schema, mutation);

  expect(result.data.createUser).toBeDefined();
  expect(result.data.createUser.id).toBeDefined();
  expect(result.data.createUser.name).toBe('Jane Doe');
  expect(result.data.createUser.email).toBe('jane.doe@example.com');
});

Conclusion

Testing GraphQL queries and mutations in JavaScript is essential to ensure the correctness of your application’s data fetching and modification functionality. By following the steps outlined in this blog post, you can effectively write and execute tests for GraphQL queries and mutations using popular testing libraries like Jest or Mocha.