Method replacement and testing utility
Often when unit testing, it is helpful to capture or replace function calls with testing code. stand-in
provides a quick and easy way to replace object methods with your own. It also provides a method to restore the original method after testing is complete.
var standin = require('stand-in');
var assert = require('assert');
var log = standin.replace(console, 'log', function (stand, value) {
assert.strictEqual(value, 'test data', 'value should equal test data');
stand.restore();
});
console.log('test data');
replace(obj, path, fn [, options])
- replacesobj[path]
withfn
where:obj
- object that has the method to replace. Will be used atthis
pointer insidefn
.path
- string path to the function to replace. Supports deep paths via "foo.bar.baz".fn
- function to replaceobj[method]
with. The first argument to this function will be a stand-in object. This is helpful if you don't want to create a holding variable.options
- an optional object supporting the following properties.startOn
- the invocation number to begin using the replacement function. Defaults to0
.stopAfter
- the final invocation number to use the replacement function. Once this number is reached, thestand-in
object willrestore()
itself. Defaults toInfinity
.
Returns a stand-in
object:
restore()
- restores the originalobj[method]
to the previous function. Generally, this will restore the method back to the initial value.original
- a handle to the original method in case you need to conditionally call it.invocations
- the number of times thestand-in
has been called.
replace
tries to prevent users from completely losing a handle to the original method. For example, you will receive an AssertionError
if you try to replace console.log
twice without first restore
ing the function first.