Contract testing in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this contract test simulation?

Consider a REST API contract test where the consumer expects a JSON response with a userId as an integer and userName as a string. The provider returns the following JSON:

{"userId": "123", "userName": "Alice"}

What will the contract test most likely report?

A Test fails due to missing userName key

B Test passes because the keys match

C Test fails due to type mismatch on userId

D Test passes because values are convertible

💡 Hint

Check the expected data types in the contract.

The contract expects userId as an integer, but the provider returns it as a string. This type mismatch causes the test to fail.

🧠 Conceptual

intermediate

Which statement best describes contract testing?

Choose the best description of contract testing in REST APIs.

A Testing the database schema behind the API

B Verifying that the API provider and consumer agree on request and response formats

C Load testing the API under heavy traffic

D Testing the UI of the API consumer application

💡 Hint

Think about what contract testing ensures between two systems.

Contract testing ensures that the API provider and consumer agree on the structure and data types of requests and responses.

🔧 Debug

advanced

Identify the cause of contract test failure

Given this contract test snippet for a REST API consumer:

expect(response).toHaveProperty('data.id');
expect(typeof response.data.id).toBe('number');
expect(response.data.name).toBeDefined();

The provider returns:

{"data": {"id": null, "name": "Bob"}}

Why does the contract test fail?

A Because <code>data.id</code> is null, not a number

B Because <code>data.name</code> is missing

C Because <code>data</code> key is missing

D Because the response is not JSON

💡 Hint

Check the expected type of data.id.

The test expects data.id to be a number, but the provider returns null, causing the failure.

📝 Syntax

advanced

Which option correctly defines a JSON schema for contract testing?

Choose the valid JSON schema snippet that requires id as an integer and name as a string in the response object.

A { "object": true, "props": { "id": { "type": "int" }, "name": { "type": "string" } }, "mandatory": ["id", "name"] }

B { "type": "object", "properties": { "id": "integer", "name": "string" }, "required": ["id", "name"] }

C { "type": "object", "fields": { "id": { "type": "int" }, "name": { "type": "str" } }, "required": ["id", "name"] }

D { "type": "object", "properties": { "id": { "type": "integer" }, "name": { "type": "string" } }, "required": ["id", "name"] }

💡 Hint

Look for correct JSON schema keywords and types.

Option D uses correct JSON schema keywords: type, properties, and required with proper types integer and string.

🚀 Application

expert

How many tests are needed to fully cover a contract with 3 optional and 2 required fields?

You have a REST API contract with 5 fields in the response: 2 are required and 3 are optional. To fully test all combinations of optional fields presence or absence along with required fields, how many distinct contract tests are needed?

A 8

B 5

C 10

D 32

💡 Hint

Think about combinations of optional fields only.

Each optional field can be present or absent independently, so 2^3 = 8 combinations. Required fields are always present, so total tests = 8.