How do you test API correctness and reliability?

API testing for correctness and reliability involves several stages:

1. Functional testing — verifying that the API returns expected responses to correct requests, handles errors and exceptions.
2. Boundary and negative testing — sending incorrect, empty, or overly large data to test stability.
3. Performance and load testing — checking how the API behaves under high load.
4. Security testing — tests for authentication, authorization, vulnerabilities (e.g., SQL injections).
5. Test automation using tools (Postman, REST Assured, JMeter) for regular reruns.

Example of a simple test to check API response using REST Assured in Java:

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

public class ApiTest {
    public void testGetUser() {
        given()
            .when().get("https://api.example.com/users/1")
            .then()
            .statusCode(200)
            .body("id", equalTo(1))
            .body("name", notNullValue());
    }
}