---
title: Chaijs Assertexpression Message
---
[@param](/users/param){ Mixed }expressionto test for truthiness  
- [@param](/users/param){ String }messageto display on error

Write your own test expressions.

    assert('foo' !== 'bar', 'foo is not bar');
    assert(Array.isArray(<a href='http://chaijs.com/api/assert/' target='_blank' rel='nofollow'>]), 'empty arrays are arrays');

details: [http://chaijs.com/api/assert/</a>