GraphQL for Testers: Basics and Testing

GraphQL is a query language for APIs: the client asks for exactly the fields it needs in one request. As a QA, you need to understand queries, mutations, and the schema so you can test GraphQL APIs effectively. This post gives you the basics and a testing angle.

GraphQL in brief

• Single endpoint: Usually one URL (e.g. POST /graphql) for all operations.
• Query: Read data (like GET). Client sends a query describing the shape of the response.
• Mutation: Change data (like POST/PUT/DELETE). Client sends a mutation with arguments and requested response shape.
• Schema: Defines types, fields, and operations. Use it to know what you can query and what to expect.

Example query and mutation

Query:

query {
  user(id: "1") {
    id
    name
    email
  }
}

Mutation:

mutation {
  createUser(input: { name: "Jane", email: "jane@example.com" }) {
    id
    name
    email
  }
}

You send these in the request body (e.g. { "query": "..." }) and check the response shape and data.

How to test GraphQL

• Positive: Valid query/mutation → 200 and data with expected shape; no errors (or expected partial errors).
• Negative: Invalid query (wrong field, wrong type) → 200 with errors array (GraphQL often returns 200 with errors in body). Test auth (e.g. unauthenticated or wrong permissions).
• Edge: Null/optional fields, empty lists, deep nesting, and large responses if relevant.

Use the schema to design tests: required vs optional fields, types, and allowed operations.

Summary

• GraphQL = single endpoint; queries for read, mutations for write; client chooses response shape.
• Use the schema to design test cases; send query/mutation in body and assert on data and errors.
• Test positive, negative, and edge cases as with REST; auth and validation still apply.