# Enforce > Fluid Assertions in Rust ## Example *Uses [stainless](https://github.com/reem/stainless) for testing syntax* ```rust describe! vec { describe! push { before_each { let mut v = vec![1u, 2, 3]; } it "should increase the length by 1" { let old = v.len(); v.push(4u); // Fluid chain with informative error messages. (enforce!(old + 1)).is().equal(v.len()); } it "should add another value to the end of the vec" { v.push(4u); // Has `some`, `none`, `ok`, and `err` methods for checking Option // and Result APIs. (enforce!(*v.get_mut(3))).is().some(); } } } ``` ### Failed Assertion ``` Enforce Error file.rs:17 - map.find("no such key") is None ``` ## License MIT