Postman: pre-request script vs Tests tab — what runs when?

Question

I keep putting logic in the wrong tab and chaining requests behaves weirdly.

Sam Okafor · Accepted Answer

Pre-request script runs BEFORE the HTTP call — use it to set headers, mint auth tokens, generate dynamic bodies. Tests script runs AFTER the response arrives — use it for assertions and to save values (pm.collectionVariables.set) for the next request in the collection runner.

// Pre-request
const token = pm.environment.get('token');
if (!token) {
  pm.sendRequest({ url: pm.environment.get('baseUrl') + '/login', method: 'POST' },
    (err, res) => pm.environment.set('token', res.json().token));
}

// Tests
pm.test('201 Created', () => pm.response.to.have.status(201));
pm.collectionVariables.set('orderId', pm.response.json().id);

Postman: pre-request script vs Tests tab — what runs when?

1 answer