Hamcrest
Matchers that can be combined to create flexible expressions of intent
Born in Java, Hamcrest now has implementations in a number of languages.
Java
Python
Ruby
Objective-C
PHP
Common Lisp
Erlang
Swift
Rust
JavaScript (JsHamcrest)
JavaScript (Hamjest)
GO (Gocrest)
C# (NHamcrest)