conversant/ad-libs.js

'use strict';

/* globals sinon */

/**
 * @desc Helper method to create Sinon.JS spies directly on the value of module.exports for a required module. To spy on a method you need access to the object it is attached to, which is problematic when the function is directly returned from a "require" call. By accessing the require.cache we can get handle to the module's exports and inject the spy.
 * @param loadedModule
 * @param {String} mockType - Defaults to 'spy'; can also be 'stub'.
 * @returns {sinon.spy}
 * @module createSpy
 * @example
 * incrementCounter.js:
 * ```js
 * module.exports = function() { ... async call ...  };
 * ```
 *
 * my-test.js
 * ```js
 * var incrementCounter = require('./incrementCounter'),
 * createSpy = require('cse-common/lib/createSpy');
 *
 * var spy = createSpy(incrementCounter);
 *
 * // test code
 * assert(spy.callCount, 4);
 * spy.restore();
 *
 * ```
 */
var createSpy = function (loadedModule, mockType) {
    mockType = mockType || 'spy';

    var spy,
        cache = require.cache,
        cachedModuleIndex,
        cachedModule;

    for (cachedModuleIndex in cache) {
        if (cache.hasOwnProperty(cachedModuleIndex)) {
            cachedModule = cache[cachedModuleIndex];

            if (cachedModule.exports === loadedModule) {
                spy = sinon[mockType](cachedModule, 'exports');
            }
        }
    }

    return spy;
};

module.exports = createSpy;