This is an example of a library. You may see a list of other libraries used on Rosetta Code at Category:Solutions by Library.
Wren-check is a module which enables one to check that a Wren value (usually a method or function argument) is of a given type or types and, where possible, within a given range of values. It can also check whether a more general condition is met, check that integer arithmetic is 'safe' (within the ± 2^53 limit) and report on the time taken to run a piece of code. It consists of four classes: Check, SafeInt, SafeInts and Benchmark, whose methods are all static.
It is the twenty-seventh in a series of modules (listed on the language's main page) designed to assist with writing Rosetta Code tasks so the same code does not have to be written or copy/pasted time and time again thereby bloating a task's script code unnecessarily.
To use it you have to copy the source code (in the talk page) to a text file called check.wren and place this in the same directory as the importing script so the command line interpreter can find it.