mattlgy/stand-in

Method replacement and testing utility

stand-in

Method replacement and testing utility

Description

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.

Usage

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]) - replaces obj[path] with fn where:
  • obj - object that has the method to replace. Will be used at this pointer inside fn.
  • path - string path to the function to replace. Supports deep paths via "foo.bar.baz".
  • fn - function to replace obj[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 to 0.
    • stopAfter - the final invocation number to use the replacement function. Once this number is reached, the stand-in object will restore() itself. Defaults to Infinity.

Returns a stand-in object:

• restore() - restores the original obj[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 the stand-in has been called.

Note

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 restoreing the function first.