Because assert and even ass were already taken!
ass-ert is a library of composable matchers offering a fluent-ish interface.
It tries to mix the best aspects of Hamcrest with its highly composable design, featuring beautifully descriptive messages, and the easy on the eyes and the fingers of chai's fluent syntax for defining assertions.
While the primary use case is testing it's by no means restricted to it, use the matchers anywhere you may have a need for matching complex data structures with ease.
If you are looking for something similar for Python have a look at pyshould!
Check out the documentation for additional details about the library.
See the license file.