Api Testing

API Testing (Playwright + REST Assured)

Comprehensive API testing skill covering both Playwright TypeScript (request fixture, Supertest, Zod) and Java (REST Assured, AssertJ, JSON Schema Validator). Provides deep domain expertise for the api-tester-specialist agent.

When to Use This Skill

• Create API tests for REST or GraphQL endpoints
• Validate request/response schemas (Zod, JSON Schema)
• Test authentication flows (OAuth2, JWT, API keys, Bearer tokens)
• Verify error handling (400, 401, 403, 404, 409, 422, 500)
• Test pagination, filtering, sorting edge cases
• Validate idempotency for PUT/DELETE operations
• Contract testing between services
• Rate limiting validation

Prerequisites

| Stack | Requirements | | ---------- | --------------------------------------------------------------------- | | TypeScript | Node.js 18+, @playwright/test or supertest, zod | | Java | Java 21+, REST Assured 5.x, AssertJ, Jackson, json-schema-validator |

Core Principles

1. Schema validation on every response — never trust an unvalidated response
2. Test all HTTP status codes — happy path AND error states
3. Auth testing is mandatory — verify 401/403 for protected endpoints
4. Data-driven — test with valid, invalid, boundary, and empty values
5. Stateless where possible — each test cleans up or uses unique data

Quick Reference — Playwright

import { test, expect } from "@playwright/test";

test("GET /api/users returns 200 with valid schema", async ({ request }) => {
  const response = await request.get("/api/users");
  expect(response.ok()).toBeTruthy();
  const body = await response.json();
  expect(body).toMatchObject({ data: expect.any(Array) });
});

Quick Reference — REST Assured

import static io.restassured.RestAssured.*;
import static org.hamcrest.Matchers.*;

import java.util.List;

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;

@Test
@DisplayName("GET /api/users returns 200 with valid schema")
void getUsers() {
    String token = "test-token";

    given()
        .header("Authorization", "Bearer " + token)
    .when()
        .get("/api/users")
    .then()
        .statusCode(200)
        .body("data", is(instanceOf(List.class)))
        .body("data.size()", greaterThan(0));
}

Common Rationalizations

> Common shortcuts and "good enough" excuses that erode test quality — and the reality behind each.

| Rationalization | Reality | | ----------------------------------------------- | ------------------------------------------------------------------------------------------------------------ | | "Schema validation is overkill" | Without schema validation, a silent field rename becomes a production incident. Validate every response. | | "Happy path testing is enough" | Error states (400, 401, 403, 404, 409, 500) are where real failures happen. Test all status codes. | | "Auth tests can wait" | Unauthenticated access to protected endpoints is a security vulnerability, not a backlog item. | | "This endpoint won't change" | APIs evolve. Contract tests catch breaking changes before they reach production. | | "Manual API testing with Postman is sufficient" | Manual testing isn't repeatable, can't run in CI, and doesn't scale. Automate API tests. | | "Idempotency doesn't matter" | Duplicate requests happen in production. Without idempotency testing, you get duplicate records and charges. |

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References

| Document | Content | | ---------------------------------------------------------------- | --------------------------------------------------- | | [REST API Patterns](./references/rest-api-patterns.md) | CRUD, pagination, filtering, error patterns | | [Playwright API Testing](./references/playwright-api-testing.md) | Request fixture, Supertest, TypeScript patterns | | [REST Assured Testing](./references/rest-assured-testing.md) | REST Assured, AssertJ, Java patterns | | [Schema Validation](./references/schema-validation.md) | Zod (TS), JSON Schema (Java), strict vs loose | | [Contract Testing](./references/contract-testing.md) | Request/response contracts, idempotency, versioning |

Templates

• [Playwright API Spec](./templates/playwright-api-spec.ts) — starter test file for API testing
• [REST Assured Test](./templates/rest-assured-test.java) — starter Java test class

Scripts

• [API Health Check](./scripts/api-health-check.sh) — validate API endpoints respond correctly

Troubleshooting

| Issue | Solution | | ------------------------------ | ------------------------------------------------------------------------------ | | 401 on authenticated endpoints | Verify token is fresh; check expiry; re-authenticate | | Flaky API tests | Add retry logic; check for rate limiting; use unique test data | | Schema validation too strict | Use .passthrough() (Zod) or additionalProperties: true for flexible fields | | Timeout on slow endpoints | Increase timeout in request options; check for server load |

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Verification

After completing this skill's workflow, confirm:

• [ ] All CRUD operations tested — POST, GET, PUT, PATCH, DELETE covered for the resource
• [ ] Status codes verified — Success (2xx) AND error codes (4xx, 5xx) tested
• [ ] Schema validation in place — Every response validated against a schema (Zod or JSON Schema)
• [ ] Authentication tested — 401 returned for protected endpoints without valid credentials
• [ ] Idempotency verified — PUT/DELETE produce same result when called multiple times
• [ ] Edge cases covered — Empty payloads, invalid types, boundary values, SQL injection attempts
• [ ] All tests pass — Playwright API tests or REST Assured tests exit successfully

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: fugazi
• Source: fugazi/test-automation-skills-agents
• License: MIT

Install and usage instructions live in the source repository linked above.