deride

deride

Mocking library based on composition

The inspiration for this was that my colleague was having a look at other mocking frameworks and mentioned to me that they do not work when using Object.freeze in the objects to enforce encapsulation. This library builds on composition to create a mocking library that can work with objects which are frozen.

Getting Started

Install the module with: npm install deride

var deride = require('deride');

Documentation

Mocking

• deride.wrap(obj)

CAUTION Remember when you use this function about the good practice recommended in the book Growing Object-Oriented Software, Guided by Tests Chapter 8: Only Mock Types That You Own

• deride.stub(methods)
  • methods Array
• deride.stub(obj)
  • obj Object
• deride.func()

Expectations

• obj.expect.method.called.times(n)
• obj.expect.method.called.once()
• obj.expect.method.called.twice()
• obj.expect.method.called.never()
• obj.expect.method.called.withArgs(args)

Resetting the counts / called with args

• obj.expect.method.called.reset()

Setup

• obj.setup.method.toDoThis(func)
• obj.setup.method.toReturn(value)
• obj.setup.method.toThrow(message)
• obj.setup.method.toCallbackWith(args)
• obj.setup.method.toTimeWarp(milliseconds)
• obj.setup.method.when(args).[toDoThis|toReturn|toThrow|toCallbackWith|toTimeWarp]

Examples

The context

var Person = function(name) {
    return Object.freeze({
        greet: function(otherPersonName) {
            console.log(name, 'says hello to', otherPersonName);
        }
    });
}

Count the number of invocations of a method

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.greet('alice');
bob.expect.greet.called.times(1);

Has convenience methods for invocation counts

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.greet('alice');
bob.expect.greet.called.once();
bob.greet('sally');
bob.expect.greet.called.twice();

Determine if a method has never been called

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.expect.greet.called.never();

Determine if a method was called with a specific set of arguments

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.greet('alice');
bob.greet('bob');
bob.expect.greet.called.withArgs('bob');

Override the method body to change the invocation

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.greet.toDoThis(function(otherPersonName) {
    return util.format('yo %s', otherPersonName);
});
var result = bob.greet('alice');
result.should.eql('yo alice');

Override the return value for a function

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.greet.toReturn('foobar');
var result = bob.greet('alice');
result.should.eql('foobar');

Force a method invocation to throw a specific error

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.greet.toThrow('BANG');
should(function() {
    bob.greet('alice');
}).
throw(/BANG/);

Override the invocation of a callback

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.chuckle.toCallbackWith([0, 'boom']);
bob.chuckle(function(err, message) {
    assert.equal(err, 0);
    assert.equal(message, 'boom');
});

Accelerating the timeout used internally by a function

var Person = function(name) {
    return Object.freeze({
        foobar: function(timeout, callback) {
            setTimeout(function() {
                callback('result');
            }, timeout);
        }
    });
};
var timeout = 10000;
var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.foobar.toTimeWarp(timeout);
bob.foobar(timeout, function(message) {
    assert.equal(message, 'result');
});

Setting the return value of a function when specific arguments are used

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.greet.when('alice').toReturn('foobar');
bob.setup.greet.toReturn('barfoo');
var result1 = bob.greet('alice');
var result2 = bob.greet('bob');
result1.should.eql('foobar');
result2.should.eql('barfoo');

Overriding a method`s body when specific arguments are provided

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.greet.when('alice').toDoThis(function(otherPersonName) {
    return util.format('yo yo %s', otherPersonName);
});
bob.setup.greet.toDoThis(function(otherPersonName) {
    return util.format('yo %s', otherPersonName);
});
var result1 = bob.greet('alice');
var result2 = bob.greet('bob');
result1.should.eql('yo yo alice');
result2.should.eql('yo bob');

Throwing an error for a method invocation when specific arguments are provided

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.greet.when('alice').toThrow('BANG');
should(function() {
    bob.greet('alice');
}).
throw (/BANG/);
should(function() {
    bob.greet('bob');
}).not.
throw (/BANG/);

Override the invocation of a callback when specific arguments are provided

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.chuckle.toCallbackWith([0, 'boom']);
bob.setup.chuckle.when('alice').toCallbackWith([0, 'bam']);
bob.chuckle(function(err, message) {
    assert.equal(err, 0);
    assert.equal(message, 'boom');
    bob.chuckle('alice', function(err, message) {
        assert.equal(err, 0);
        assert.equal(message, 'bam');
    });
});

Accelerating the timeout used internally by a function when specific arguments are provided

var Person = function(name) {
    return Object.freeze({
        foobar: function(timeout, callback) {
            setTimeout(function() {
                callback('result');
            }, timeout);
        }
    });
};
var timeout1 = 10000;
var timeout2 = 20000;
var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.foobar.toTimeWarp(timeout1);
bob.setup.foobar.when(timeout2).toTimeWarp(timeout2);
bob.foobar(timeout1, function(message) {
    assert.equal(message, 'result');
    bob.foobar(timeout2, function(message) {
        assert.equal(message, 'result');
        done();
    });
});

Creating a stubbed object

Stubbing an object simply creates an anonymous object, with all the method specified and then the object is wrapped to provide all the expectation functionality of the library

var bob = deride.stub(['greet']);
bob.greet('alice');
bob.expect.greet.called.times(1);

Creating a stubbed object based on an existing object

var Person = {
    greet: function(name) {
        return 'alice sas hello to ' + name;
    },
};
var bob = deride.stub(Person);
bob.greet('alice');
bob.expect.greet.called.once();

Creating a single mocked method

var func = deride.func();
func.setup.toReturn(1);
var value = func(1, 2, 3);
assert.equal(value, 1);

Force the emit of an event on an object

var bob = deride.stub([]);
bob.on('message', function() {
    done();
});
bob.emit('message', 'payload');

Contributing

Please ensure that you run grunt, have no style warnings and that all the tests are passing.

License

Copyright (c) 2014 Andrew Rea
Copyright (c) 2014 James Allen

Licensed under the MIT license.