API Testing

API Testing with Postman + Newman

Generate API tests as Postman collections. Run them with Newman CLI.

Setup

npm install -g newman

Test Pattern

Each request gets tests in the Tests tab:

// Assert status code
pm.test("Status is 200", function () {
    pm.response.to.have.status(200);
});

// Assert response body
pm.test("Returns user name", function () {
    pm.expect(pm.response.json().name).to.eql("Test User");
});

// Assert response time
pm.test("Response under 2s", function () {
    pm.expect(pm.response.responseTime).to.be.below(2000);
});

// Validate schema
pm.test("Matches schema", function () {
    pm.response.to.have.jsonSchema({
        type: "object",
        required: ["id", "name", "email"],
        properties: {
            id: { type: "number" },
            name: { type: "string" },
            email: { type: "string" }
        }
    });
});

Pass Data Between Requests

Save a value from one response, use it in the next:

// In POST /users Tests tab — save created ID
const id = pm.response.json().id;
pm.environment.set("created_id", id);

// In GET /users/{{created_id}} — it auto-resolves

Negative Tests

// Missing required field → expect 400 or 422
pm.test("Rejects missing field", function () {
    pm.expect(pm.response.code).to.be.oneOf([400, 422]);
});

// No auth token → expect 401
pm.test("Rejects unauthorized", function () {
    pm.response.to.have.status(401);
});

Run with Newman

# Basic run
newman run collection.json

# With environment
newman run collection.json -e environment.json

# Override variables
newman run collection.json --env-var "base_url=https://staging.example.com"

# Data-driven from CSV
newman run collection.json -d testdata.csv

# CI report
newman run collection.json -r junit --reporter-junit-export report.xml

Guidelines

• Use environment variables for base_url and secrets, never hardcode.
• One assertion per pm.test block.
• Assert status code first, then body.
• Export collections as v2.1 format.

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