prunk

A mocking utility for node.js require

Author: Daniel Koch
Version: 1.3.1

Copyright 2016 Daniel Koch

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

Require node’s module module that provides access to all the things require() uses

var Module = require('module');

_load

The original module._load function

var _load = void 0;

cache

The cache that contains mocks and suppressed imports

var cache = [];

init

Overwrites Module._load with a function that either returns a mocked value from the cache or whatever the original function returns if nothing has been mocked.

var init = function() {
    _load = Module._load;

Overwrite the original _load function The important argument for us is req because its the name of whatever was required.

    Module._load = function(req, parent, isMain) {

Take the cache…

        var mock = cache

Find the tests that match

                        .filter(function(mockDef) {
                            var test = mockDef.test;

If we have a regex we match it against the string

                            if( test instanceof RegExp )
                                return null !== req.match( test );

If we have a function we let the function decide

                            if( 'function' === typeof test )
                                return !! test(req, parent, isMain);

If there is an alias we check if the string starts with the desired test

                            if( 'alias' === mockDef._type )
                                return req.startsWith( mockDef.test );

Last case: we simply have no idea Thus, we use a strict equal

                            return test === req;
                        });

If we found a mocked import we return it. We only use the first mock we find. Since the createMock() function uses Array.prototype.unshift we always use the mock added at last.

        if( mock.length ) {
            mock = mock[0];
            value = mock.value;

Aliases are a bit special

            if( 'alias' !== mock._type )
                return value;

If the alias is a function we let that function do the transformation of the path

            if( 'function' === typeof value )
                req = value(req);

If it is not a function we use string replacement

            else
                req = req.replace(mock.test, value);
        }

No mock; let the load system do its work

        return _load.call(Module, req, parent, isMain);
    };
};

createMock

Creates a mock with the given test, mocking with the given value and use the given type.

• test - Something that is used to compare. Might be a string, a function or something else
• value - The mock value that replaces the original import
• type - Type, either 'mock' or 'sup'. This is used to remove it later on.

var createMock = function(test, value, type) {

Initialize the cache if not done already

    if( ! _load )
        init.call(this);

Push the new item to the front

    cache.unshift({
        test: test,
        value: value,
        _type: type
    })
};

remove

Removes a mock definition from the collection.

• test - Something that is used to compare. Might be a string, a function or something else
• type - Type, either 'mock' or 'sup'.

var remove = function(test, type) {

We want to use strict equals below thus we use the string representation of RegExp’s

    if( test instanceof RegExp )
            test = ('' + test);

    cache = cache.filter( function(def) {

If the type does not match we ignore it

            if( type !== def._type )
                return true;

Again, convert RegExp’s if found

            var cmp = (def.test instanceof RegExp) ? '' + def.test : def.test;

            return test !== cmp;
        });
};

removeAll

Removes all mocks of the given type

• type - Type, either 'mock' or 'sup'.

var removeAll = function(type) {
    cache = cache.filter( function(item) {
        return item._type !== type;
    });
};

The prunk object

var prunk = {

Provide access to the cache. This is done to make the testing more reliable.

    get _cache() {
        return cache;
    },

    set _cache(what) {
        cache = what;
    },

mock

Mocks the given import with the given value. test can be a function that is used to compare whatever is required and returns true or false. If the return value is truthy the import will be mocked with the given value.

The function’s arguments are the same as with Module._load. Most of the time you will look at the first argument, a string.

var mockStyles = (req) => 'style.css' === req;
prunk.mock( mockStyles, 'no css, dude.');

test can also be a RegExp that is matched agains the name of the import or a string. It can be anything else, too, if your imports are gone totally crazy.

prunk.mock( 'style.css', 'no css, dude.' );
prunk.mock( /\.(css|scss|sass|less)/, 'no styles, dude.');

It returns the prunk object so that you can chain calls.

    mock: function(test, value) {
        createMock(test, value, 'mock');
        return prunk;
    },

suppress

Suppresses the given import. A suppressed import always returns undefined. The test argument is the same as used by mock().

It returns the prunk object so that you can chain calls.

    suppress: function(test) {
        createMock(test, void 0, 'sup');
        return prunk;
    },

unmock

Removes the mock registered for the given test. unmock() uses strict equal to compare the registered mocks. It returns the prunk object so that you can chain calls.

    unmock: function(test) {
        remove(test, 'mock');
        return prunk;
    },

unsuppress

Removes the mock registered for the given test. unsuppress() uses strict equal to compare the suppressed imports. It returns the prunk object so that you can chain calls.

    unsuppress: function(test) {
        remove(test, 'sup');
        return prunk;
    },

unmockAll

Removes all mocks for imports It returns the prunk object so that you can chain calls.

    unmockAll: function() {
        removeAll('mock');
        return prunk;
    },

unsuppressAll

Removes all suppressed imports It returns the prunk object so that you can chain calls.

    unsuppressAll: function() {
        removeAll('sup');
        return prunk;
    },

alias

Aliases a path that begins with the given string or matches the given regex. This basically performs a string replacement if you provide a simple string or a regex. The regular expressions must contain at least one grouping expression (...) so that the replacement actually happens. alias can also be a function that gets the path and returns an updated one. You can only provide a predicate function for test if alias is also a function returning a modified path. This method will throw if arguments are invalid.

    alias: function(test, alias) {

        if( 'undefined' === typeof alias )
            throw new Error('prunk.alias needs a second argument');

        if( 'function' === typeof test && 'function' !== typeof alias )
            throw new Error('prunk.alias has been passed a function as test but not as alias');

        if( test instanceof RegExp && ! test.toString().includes('(') )
            throw new Error('prunk.alias has been passed a RegExp without a grouping expression');

        createMock(test, alias, 'alias');
        return prunk;
    },

unalias

Removes the alias for the given test It returns the prunk object so that you can chain calls.

    unalias: function(test) {
        remove(test, 'alias');
        return prunk;
    },

unaliasAll

Removes all aliases It returns the prunk object so that you can chain calls.

    unaliasAll: function() {
        removeAll('alias');
        return prunk;
    },

teardown

Removes all aliases as well as all mocked and suppressed imports

    teardown: function() {
        this.unaliasAll();
        this.unsuppressAll();
        this.unmockAll();
    }

};

Exports

module.exports = prunk;