catch-and-match

A simple utility for testing and inspecting an error thrown (a)synchronously by a function.

Made with ❤ at @outlandish

Install

npm install catch-and-match --save-dev

Catch and Match

Sometimes asserting that something just throws isn't enough. catch-and-match allows you to assert that a function which should throw throws the error you expect. This is particularly useful for testing functions that produce error messages which provide useful feedback (the best kind of modules!).

Usage

catchAndMatch(fn, matcher[, cb])

fn {Function} function that should throw traditionally or within a Promise

• if fn does not throw, catch and match returns a rejected Promise and calls cb with an error as its first argument
• if fn throws the error is tested against matcher (see below)

matcher {RegExp|String|Function} method of inspecting error:

• a Function is passed the Error and should return true when the test should pass
• a String is turned to simple RegExp (new RegExp(str))
• a RegExp is tested against the Error message (re.test(err.message))

cb {Function} error-first callback indicating success of catch and match

Examples

function log (str) {
    if (typeof str !== 'string') {
        throw new Error('str should be a string');
    }
    console.log(str);
}

// Passes with string matcher
it('should throw an error without correct arguments', function (cb) {
    catchAndMatch(log.bind(undefined, 'hello'), /should be a string/, cb);
    // or, using Promises:
    // return catchAndMatch(log.bind(undefined, 'hello'));
});

// Fails with RegExp matcher
it('should throw an error without correct arguments', function (cb) {
    catchAndMatch(log.bind(undefined, 10), /should be a string/, cb);
    // or, using Promises:
    // return catchAndMatch(log.bind(undefined, 10));
});

// Passes with function matcher
it('should throw an error without correct arguments', function () {
    return catchAndMatch(log.bind(undefined, 10), function (err) {
        return err.includes('should be a string');
    });
});