Snapshot testing queries in GraphQL - Mini Project: Build & Apply

Snapshot Testing Queries

📖 Scenario: You are working on a GraphQL API for a bookstore. You want to ensure that your queries return consistent data over time. Snapshot testing helps you capture the current output of a query and compare it automatically in future tests.

🎯 Goal: Build a simple GraphQL query and set up a snapshot test to capture its output. This will help you verify that the query results do not change unexpectedly.

📋 What You'll Learn

Create a GraphQL query named GetBooks that fetches id, title, and author fields from books.

Define a variable called snapshotName with the value BooksQuerySnapshot.

Write a function called runQuery that executes the GetBooks query.

Add a final step to save the query result to a snapshot using the snapshotName.

💡 Why This Matters

🌍 Real World

Snapshot testing is used in real projects to catch unexpected changes in API responses, ensuring frontend and backend stay in sync.

💼 Career

Understanding snapshot testing of GraphQL queries is valuable for roles in frontend development, backend API development, and quality assurance.

1

Create the GraphQL query

Write a GraphQL query called GetBooks that fetches id, title, and author fields from the books type.

GraphQL

# Write the GraphQL query 'GetBooks' here
# Your code here

Hint

Use the query keyword followed by GetBooks. Inside, request the books field with id, title, and author subfields.

2

Define the snapshot name variable

Create a variable called snapshotName and set it to the string "BooksQuerySnapshot".

GraphQL

query GetBooks {
  books {
    id
    title
    author
  }
}

# Define the variable 'snapshotName' here
# Your code here

Hint

Use const snapshotName = "BooksQuerySnapshot"; to define the variable.

3

Write the query execution function

Write a function called runQuery that executes the GetBooks query and returns the result. Use an async function and assume a graphqlClient object with a query method.

GraphQL

query GetBooks {
  books {
    id
    title
    author
  }
}

const snapshotName = "BooksQuerySnapshot";

# Write the async function 'runQuery' here
# Your code here

Hint

Define an async function named runQuery. Inside, use await graphqlClient.query({ query: GetBooks }) and return result.data.

4

Save the query result to a snapshot

Add code to call runQuery and save its result to a snapshot using the variable snapshotName. Assume a function saveSnapshot(name, data) is available.

GraphQL

import { gql } from '@apollo/client';

const GetBooks = gql`
  query GetBooks {
    books {
      id
      title
      author
    }
  }
`;

const snapshotName = "BooksQuerySnapshot";

async function runQuery() {
  const result = await graphqlClient.query({ query: GetBooks });
  return result.data;
}

# Call runQuery and save the result to a snapshot using 'saveSnapshot(snapshotName, data)'
# Your code here

Hint

Use runQuery().then(data => saveSnapshot(snapshotName, data)); to save the snapshot.

Practice

1. What is the main purpose of snapshot testing in GraphQL queries?

easy

A. To improve the speed of GraphQL queries

B. To generate new GraphQL schemas

C. To detect unexpected changes in query results automatically

D. To optimize database indexing

Solution

1. Step 1: Understand snapshot testing concept

   Snapshot testing captures the output of a query at a point in time to compare later.

2. Step 2: Identify the purpose in GraphQL context

   It helps catch unexpected changes in the query results automatically during tests.

3. Final Answer:

   To detect unexpected changes in query results automatically -> Option C

4. Quick Check:

   Snapshot testing = detect changes automatically [OK]

Hint: Snapshot testing checks if query results change unexpectedly [OK]

Common Mistakes:

• Thinking snapshot testing speeds up queries
• Confusing snapshot testing with schema generation
• Assuming it optimizes database indexes

2. Which of the following is the correct syntax to write a simple GraphQL query for snapshot testing user names and emails?

easy

A. query { users name email }

B. query users { name, email }

C. { users: name, email }

D. query { users { name, email } }

Solution

1. Step 1: Recall GraphQL query syntax

   A valid query starts with 'query' keyword, then braces with fields selected properly.

2. Step 2: Check each option's syntax

   query { users { name, email } } correctly uses 'query { users { name, email } }' with nested braces for fields.

3. Final Answer:

   query { users { name, email } } -> Option D

4. Quick Check:

   Correct GraphQL query syntax = query { users { name, email } } [OK]

Hint: GraphQL queries need nested braces for fields inside objects [OK]

Common Mistakes:

• Missing braces around fields
• Incorrect use of colon or commas
• Omitting 'query' keyword or braces

3. Given this GraphQL query for snapshot testing:
query { posts { id title author { name } } }
What will be the shape of the returned JSON data?

medium

A. {"data":{"posts":[{"id":1,"title":"Hello","author":{"name":"Alice"}}]}}

B. {"posts":[{"id":1,"title":"Hello","author":{"name":"Alice"}}]}

C. {"data":{"posts":{"id":1,"title":"Hello","author":{"name":"Alice"}}}}

D. {"data":{"posts":[{"id":1,"title":"Hello","author":"Alice"}]}}

Solution

1. Step 1: Understand GraphQL response format

   GraphQL responses wrap results inside a 'data' object, with arrays for list fields.

2. Step 2: Analyze the query structure

   'posts' is a list, so its value is an array of objects with 'id', 'title', and nested 'author' object.

3. Final Answer:

   {"data":{"posts":[{"id":1,"title":"Hello","author":{"name":"Alice"}}]}} -> Option A

4. Quick Check:

   GraphQL response = data object with arrays for lists [OK]

Hint: GraphQL responses always wrap data inside a 'data' field [OK]

Common Mistakes:

• Omitting the 'data' wrapper
• Using object instead of array for list fields
• Flattening nested objects incorrectly

4. You wrote this snapshot test query:
query { user { id name email } }
But the test fails with an error: "Cannot query field 'user' on type 'Query'".
What is the most likely cause?

medium

A. The schema does not have a 'user' field on the root Query type

B. The query is missing the 'query' keyword

C. The fields inside 'user' are invalid

D. Snapshot testing does not support nested fields

Solution

1. Step 1: Interpret the error message

   The error says 'user' field is not found on the root Query type in the schema.

2. Step 2: Check query syntax and schema

   The query syntax is valid, so the problem is likely the schema missing 'user' field.

3. Final Answer:

   The schema does not have a 'user' field on the root Query type -> Option A

4. Quick Check:

   Field missing in schema = The schema does not have a 'user' field on the root Query type [OK]

Hint: Check schema fields if query field causes 'Cannot query field' error [OK]

Common Mistakes:

• Assuming missing 'query' keyword causes this error
• Blaming nested fields without schema check
• Thinking snapshot testing limits field nesting

5. You want to create a snapshot test for a GraphQL query that fetches a list of products with their id, name, and price, but only for products priced above $50.
Which query correctly applies this filter for snapshot testing?

hard

A. query { products(filter: { price: { gt: 50 } }) { id name price } }

B. query { products(filter: { price_gt: 50 }) { id name price } }

C. query { products { id name price if price > 50 } }

D. query { products { id name price where price > 50 } }

Solution

1. Step 1: Understand GraphQL filtering syntax

   Filters are usually passed as arguments with field names and operators like 'price_gt' for greater than.

2. Step 2: Evaluate each option's filter usage

   query { products(filter: { price_gt: 50 }) { id name price } } uses 'filter: { price_gt: 50 }' which is a common and correct pattern.

3. Final Answer:

   query { products(filter: { price_gt: 50 }) { id name price } } -> Option B

4. Quick Check:

   Use filter arguments with operator suffixes like _gt [OK]

Hint: Use filter arguments with _gt for greater than in GraphQL [OK]

Common Mistakes:

• Placing conditions inside selection sets
• Using invalid keywords like 'where' or 'if' inside query
• Incorrect nested filter object structure