ass-ert documentation

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.

Some core concepts

Without going into the internals of the library, just to be able to understand correctly the language in the documentation, these are some of terms and concepts used:

Matcher

abstract definition of some test (i.e. "equals something").

Expectation

concrete instance of a matcher (i.e. "equals 10").

Expression

chain of expectations (1 or more) that are evaluated from left to right and stops on the first expectation that fails.

Resolver

the algorithm that traverses an expression and produces a boolean result from it.

Subject

refers to the value we're testing the expression against.

Unless you want to create your own matchers the only concept you'll be working with are expressions. An expression can have three possible results when resolved:

true

All the expectations were run and tested that the data was valid

false

One of the expectations failed its test on the data. Since expressions are short-circuited, not all the expectations are guaranteed to have been tested, this is similar to most programming languages so it should be a familiar behaviour (ie: false && work(), work is never executed).

undefined

An asynchronous expectation (i.e. Promises) has taken control of the resolver and it'll produce a true/false result at a later point via the own Promises/A interface of the expression.

ass = require('ass-ert');
console.log(ass.help);