Testing with Postman: Chai Assertions
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I build automation frameworks — not just tests.
Over 10 years I've designed and shipped production testing platforms across payment, insurance, and healthcare domains. My instinct is always toward architecture: clean abstractions, maintainable patterns, and systems that don't fall apart when the product scales.
What I'm working on now:
- A Claude/Playwright agent framework that generates test cases directly from Jira tickets
- Concurrency and race-condition coverage for financial transactions
- A modular Playwright/JavaScript platform covering UI and 20+ API service integrations with 100+ JSON schema validators
I've built production automation in Playwright, Geb/Spock, Rest-Assured, and Selenium across payment, insurance, and healthcare domains. When a stack isn't working, I replace it. When a pattern is wrong, I fix it.
If the automation problem is interesting, I'm probably already thinking about it.
Postman uses the Chai Assertion Library so familiarize yourself with it.
Using Chai Match Assertion
You can define a format for your response using Regex and the match assertion. Below is an example of a data format for a mysql date.
Date Format
pm.test("Date is correct format", function() {
pm.expect(jsonData.date).to.match(/^\\d{4}-\\d{2}-\\d{2}T\\d{2}:\\d{2}:\\d{2}Z$/, "Date should be 0000-00-00T00:00:00Z not " + jsonData.date);
});
Multiple Assertions
When using multiple assertions on a single data point you don't need to create an a new pm.expect. Instead use and and a proper error message. Since a proper error message is there you will know what has happened.
And
pm.expect(jsonData.smallsString).to.be.a('string', 'smallsString is not a string')
.and.be.lengthOf(5, 'smallsString is not 5 in length')
.and.to.contain('den', 'smallsString does not contain den')
See the below Chai Assertion Library link for more on Chai Assertions.
Links
Postman Quick Reference Guide Chai Assertion Library Regex Cheat Sheet Postman: The Complete Guide on Udemy
