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Powerful JavaScript mocking

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Install it

npm install pretendr.

Use it

var pretendr = require('pretendr');

Mock your objects. You can pass in real objects (pretendr(require("fs"))) but I prefer to keep mocks to a minimum so I know exactly what my code is doing.

var mockFs = pretendr({
    appendFile : function () {},
    createReadStream : function () {},
    readFile : function () {},
    readFileSync : function () {}

Each function creates a mock function and each object creates a mock object. (As a shortcut, pretendr() creates a standalone mock function which you can use as a dummy callback.)

mockFs now contains a mock property, which is what you pass in to your code for testing as a substitute for the real thing. This is virtually indistinguishable to your code from the object you are mocking.

var fs = mockFs.mock;
fs.readFile('f.txt', cb);

It works well with injectr, which allows you to pass in your mocks when testing.

var myLib = injectr("../lib/mylib.js", {
    fs : mockFs.mock

Or you can use whichever dependency injection method you're used to.

Now let's monitor the calls:

assert.equal(fs.readFile.calls[0].args[1], 'f.txt');
assert.equal(fs.appendFile.calls.length, 0);

And run the callback, then test that it did what we expect:

assert.equal(fs.appendFile.calls.length, 1);

We can set return values:

mockFs.readFileSync.returnValue("some text");
// or 
mockFs.readFileSync.fake(function () {
    // arguments and context are correctly passed to this function 
    return "some text";

Templates allow you to create a new pretendr object each time the function is run:

    on : function () {}

Then retrieve your created pretendr:

var mockRs = mockFs.createReadStream.calls[0].pretendr;
assert.equal(mockRs.calls[0].args[0], "data");

If you have lots of function calls and you only want to test one of them, use findCall to find a call by it's arguments:


findCall can also take a number for a number of arguments, or a function which should return true for each matching argument.

Share it

pretendr is under the MIT License. Fork it. Modify it. Pass it around.