Mock server limitations in Postman - Build an Automation Script

Verify mock server returns correct response and handles unsupported methods

Preconditions (3)

Step 1: Send a GET request to the mock server endpoint /user

Step 2: Verify the response status code is 200

Step 3: Verify the response body contains the expected JSON data

Step 4: Send a POST request to the mock server endpoint /user

Step 5: Verify the response status code is 404 or appropriate error indicating unsupported method

✅ Expected Result: The mock server returns the correct JSON response for GET /user with status 200, and returns an error status for unsupported POST /user request

Automation Requirements - Postman test scripts

Assertions Needed:

Response status code is 200 for GET /user

Response body matches expected JSON for GET /user

Response status code is 404 or error for POST /user

Best Practices:

Use pm.test and pm.response assertions

Use environment variables for mock server URL

Separate tests for different HTTP methods

Check both status code and response body

Automated Solution

Postman

const mockServerUrl = pm.environment.get('mockServerUrl');

// Test GET /user
pm.test('GET /user returns 200 and expected JSON', async () => {
    const getResponse = await pm.sendRequest({
        url: `${mockServerUrl}/user`,
        method: 'GET'
    });
    pm.expect(getResponse).to.have.property('code', 200);
    pm.expect(getResponse.json()).to.deep.equal({"id": 1, "name": "John Doe"});
});

// Test POST /user unsupported method
pm.test('POST /user returns error status for unsupported method', async () => {
    const postResponse = await pm.sendRequest({
        url: `${mockServerUrl}/user`,
        method: 'POST',
        body: {
            mode: 'raw',
            raw: JSON.stringify({"id": 2, "name": "Jane"})
        }
    });
    pm.expect(postResponse.code).to.be.oneOf([404, 405]);
});

This Postman test script uses pm.sendRequest to send HTTP requests to the mock server URL stored in an environment variable.

First, it sends a GET request to /user and asserts the response status code is 200 and the JSON body matches the expected user data.

Second, it sends a POST request to the same endpoint, which is unsupported by the mock server, and asserts the response status code is either 404 or 405, indicating the method is not allowed.

Using pm.test groups assertions clearly, and pm.expect checks the response properties. This approach verifies mock server limitations on supported HTTP methods.

Common Mistakes - 3 Pitfalls

Hardcoding the mock server URL inside the test script

Not checking the response status code for unsupported methods

Using synchronous pm.sendRequest calls without waiting for response

Bonus Challenge

Now add data-driven testing with 3 different user IDs for GET /user endpoint

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