How do I parameterize API test cases for multiple inputs?

Parameterizing API test cases means running the same test logic with different input sets and expected results. The exact method depends on your test framework, but the general approach is:

1. Define your test data

Create a table/list of cases with:

• input payloads
• path/query params
• headers
• expected status codes
• expected response fields

Example:

Case	Input	Expected Status
valid user	{"name":"Ana","age":30}	201
missing name	{"age":30}	400
invalid age	{"name":"Ana","age":"abc"}	400

2. Write one reusable test

Your test should accept parameters and assert outcomes based on them.

Pseudo-example:

def test_create_user(payload, expected_status):
    response = api.post("/users", json=payload)
    assert response.status_code == expected_status

3. Feed multiple cases into the test

Use your framework’s parameterization feature.

Pytest example

import pytest

@pytest.mark.parametrize("payload, expected_status", [
    ({"name": "Ana", "age": 30}, 201),
    ({"age": 30}, 400),
    ({"name": "Ana", "age": "abc"}, 400),
])
def test_create_user(payload, expected_status):
    response = client.post("/users", json=payload)
    assert response.status_code == expected_status

JUnit 5 example

@ParameterizedTest
@MethodSource("userCases")
void testCreateUser(Map<String, Object> payload, int expectedStatus) {
    Response response = given()
        .body(payload)
        .when().post("/users");

    assertEquals(expectedStatus, response.statusCode());
}

Postman/Newman

Use:

• CSV/JSON data files in the collection runner
• variable substitution like {{name}}, {{age}}

4. Keep assertions data-driven

For each case, validate:

• status code
• error message
• schema
• important response fields
• side effects if needed

5. Best practices

• Keep each case independent
• Name cases clearly
• Cover positive, negative, and boundary inputs
• Use fixtures/helpers for setup/teardown
• Avoid overloading one parameterized test with too many unrelated assertions

If you want, I can show you how to do this in a specific tool like pytest, JUnit, REST Assured, Postman, Karate, or Playwright.