What Is API Testing?
API testing checks that each endpoint returns the right data, status codes and errors for valid and invalid requests, and that it works correctly with databases and other services. Because it skips the user interface, API testing is faster and more stable than browser testing, and it catches most backend bugs.
Types of API Tests
Type | What it checks |
Functional | Each endpoint returns the right result for valid requests |
Negative | Invalid input, missing fields and wrong types are rejected properly |
Contract | Responses match the agreed schema, such as an OpenAPI spec |
Integration | Endpoints work with the database, queues and external services |
Authorization | Users can only reach their own data. See API Security |
Performance | Endpoints stay fast under load. See Performance Engineering |
This Is For You If...
Backend changes break your frontend or mobile app
Partners or customers integrate with your API
You don't have tests that run against your endpoints
Your OpenAPI or GraphQL schema and real behavior have drifted apart
Bugs show up as 500 errors in production
What We Build
Endpoint Test Suites
Tests for every critical endpoint with Postman/Newman, pytest, Jest with Supertest, or REST Assured.
Contract Tests
Schema validation against your OpenAPI spec or GraphQL schema. See API Design.
Test Data
Seeded databases and fixtures that make tests repeatable.
CI Integration
API tests run on every pull request. See Test Automation.
Common Mistakes to Avoid
Instinct | Why It Doesn't Help | Do This Instead |
Testing only successful requests | Error handling breaks unnoticed | Add negative and edge-case tests |
Testing against shared staging data | Tests fail randomly | Use isolated, seeded test data |
Checking status codes only | Wrong data still passes | Assert on response bodies and schemas |
Manual Postman runs | Tests aren't run consistently | Run collections automatically in CI |
How It Works
1. Inventory
List endpoints and their consumers
2. Prioritize
Rank by business impact and change frequency
3. Write tests
Functional, negative and contract tests
4. Automate
Run in CI with reports
5. Maintain
Update tests with every API change
Why Codersarts
We design and build APIs as well as test them, so tests reflect how your API should behave, not just what it does today.
Turnaround Time
API tests for up to about 30 endpoints usually take 2 to 5 working days, including CI setup.
FAQ
Which tools do you use for API testing?
Postman with Newman, pytest, Jest with Supertest, REST Assured and k6, depending on your stack.
Do you test GraphQL APIs?
Yes, including queries, mutations, errors and schema changes.
Is API testing the same as API security testing?
No. Functional API testing checks correct behavior; security testing checks for vulnerabilities. See API Security.
Can you generate tests from our OpenAPI spec?
Yes, as a starting point, then we add business-specific checks.
Is our project kept confidential?
Yes. Your code, data, and test results stay confidential, and an NDA is available on request.
Fixed-Price Tasks to Start With
API Test Suite Setup: automated tests for your endpoints
CI Test Pipeline Setup: run them on every change
Related Services
Would You Know If an Endpoint Broke Today?
Build API tests that tell you within minutes.