deride

Mocking library based on composition

  • deride

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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
- methods Array - obj Object

Expectations


All of the above can be negated e.g. negating the .withArgs would be:
  • ``obj`.expect.`method`.called.not`.withArgs(args)

Resetting the counts / called with args

Setup

Examples

The context

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

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 with properties

To stub an object with pre set properties call the stub method with a properties array in the second parameter. We are following the defineProperty definition as can be found in the below link.
https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/GlobalObjects/Object/defineProperty
var bob = deride.stub(['greet'], [{name: 'age', options: { value: 25, enumerable: true}}]);
bob.age === 25;

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);

Wrapping an existing function

var f = function (name) { return 'hello ' + name; };
var func = deride.func(f);
assert(func('bob'), 'hello bob');
func.expect.called.withArg('bob');

Wrapping an existing promise function

var f = function (name) { return 'hello ' + name; };
var func = deride.func(when.lift(f));
func('bob').then(function (result) {
    assert(result, 'hello bob');
    func.expect.called.withArg('bob');
}).finally(done);

Events

Force the emit of an event on an object

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

Emit an event on method invocation

bob.setup.greet.toEmit('testing');
bob.on('testing', function() {
	done();
});
bob.greet('bob');

Emit an event with args on method invocation

bob.setup.greet.toEmit('testing', 'arg1', { a: 1 });
bob.on('testing', function(a1, a2) {
	a1.should.eql('arg1');
	a2.should.eql({ a: 1 });
	done();
});
bob.greet('bob');

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();

Handy lt, lte, gt and gte methods

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

bob.expect.greet.called.lt(4);
bob.expect.greet.called.lte(3);
bob.expect.greet.called.gt(2);
bob.expect.greet.called.gte(3);

Determine if a method has never been called

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

Resetting the called count on all methods

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

bob.called.reset();

bob.expect.greet.called.never();
bob.expect.echo.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');

Determine if a method was called with the exact set of arguments

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.greet('alice', ['james'], 987);
bob.expect.greet.called.matchExactly('alice', ['james'], 987);

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');

Overriding the promise resolver for a function

To resolve with a value

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.greet.toResolveWith('foobar');
bob.greet('alice').then(function(result) {
    result.should.eql('foobar');
});

To reject with a value

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.greet.toRejectWith('foobar');
bob.greet('alice').catch(function(result) {
    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

when there is only one function passed as args

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');
});

when the callback is the last arg which is a function

var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.chuckle.toCallbackWith(0, 'boom');
bob.chuckle('bob', function() {
    done('this was not the callback');
}, function(err, message) {
    assert.equal(err, 0);
    assert.equal(message, 'boom');
    done();
});

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');
});

Setup an intercept

Currently this will allow you to inspect the arguments that are passed to a method, but it will not pass any modifications to the real method.
var bob = new Person('bob');
bob = deride.wrap(bob);
bob.setup.greet.toIntercept(function () {
    console.log(arguments); // { '0': 'sally', '1': { message: 'hello %s'} }
});

bob.greet('sally', {message: 'hello %s'});

Setup for specific arguments

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();
    });
});

Use a function as a predicate

If a function is passed to the when, then this will be invoked with the arguments passed. The function that has been setup will be called if this predicate returns truthy.
function resourceMatchingPredicate(msg) {
	var content = JSON.parse(msg.content.toString());
	return content.resource === 'talula';
}
bob.setup.chuckle.toReturn('chuckling');
bob.setup.chuckle.when(resourceMatchingPredicate).toReturn('chuckle talula');

var matchingMsg = {
	//...
	//other properties that we do not know until runtime
	//...
	content: new Buffer(JSON.stringify({
		resource: 'talula'
	}))
};
bob.chuckle(matchingMsg).should.eql('chuckle talula');

Setting multiple functions as a predicates

function tatulaMatchingPredicate(msg) {
	var content = JSON.parse(msg.content.toString());
	return content.resource === 'talula';
}
function babulaMatchingPredicate(msg) {
	var content = JSON.parse(msg.content.toString());
	return content.resource === 'babula';
}
bob.setup.chuckle.toReturn('chuckling');
bob.setup.chuckle.when(tatulaMatchingPredicate).toReturn('chuckle talula');
bob.setup.chuckle.when(babulaMatchingPredicate).toReturn('chuckle babula');

var matchingMsg = {
	//...
	//other properties that we do not know until runtime
	//...
	content: new Buffer(JSON.stringify({
		resource: 'talula'
	}))
};
bob.chuckle(matchingMsg).should.eql('chuckle talula');
matchingMsg.content.resource = 'babula';
bob.chuckle(matchingMsg).should.eql('chuckle babula');

Setup for multiple invocations

Using a stub X times

bob.setup.greet
    .toReturn('alice')
    .twice()
    .and.then
    .toReturn('sally');
bob.greet().should.eql('alice');
bob.greet().should.eql('alice');
bob.greet().should.eql('sally');
bob.greet().should.eql('sally');

Using a stub when

var normalResult = bob.greet('talula');
var normalSimon = bob.greet('simon');
bob.setup.greet
    .when('simon')
    .toReturn('alice')
    .twice();
// default Person behaviour
should(bob.greet('talula')).eql(normalResult);
// overridden behaviour
bob.greet('simon').should.eql('alice');
bob.greet('simon').should.eql('alice');
// default Person behaviour
should(bob.greet('simon')).eql(normalSimon);

Specify to fallback

var normalResult = bob.greet('alice');
debug('normalResult', normalResult);
bob.setup.greet
    .toReturn('alice')
    .twice()
    .and.then
    .fallback();
bob.greet('alice').should.eql('alice');
bob.greet('alice').should.eql('alice');
should(bob.greet('alice')).eql(normalResult);

Provide access to individual calls to a method

var bob = deride.wrap(bob);
bob.greet('jack', 'alice');
bob.greet('bob');
bob.expect.greet.invocation(0).withArg('alice');
bob.expect.greet.invocation(1).withArg('bob');

Enable the assertion on a single arg being used in any invocation

when the arg is a primitive object

var bob = deride.wrap(bob);
bob.greet('alice', {
    name: 'bob',
    a: 1
}, 'sam');
bob.expect.greet.called.withArg('sam');

when the arg is not a primitive object

var bob = deride.wrap(bob);
bob.greet('alice', {
    name: 'bob',
    a: 1
});
bob.expect.greet.called.withArg({
    name: 'bob'
});

Use a RexExp match for the assertion on any args being used in any invocation

when the arg is a primitive object

var bob = deride.stub(['greet']);
bob.greet('The inspiration for this was that my colleague was having a');
bob.greet({a: 123, b: 'talula'}, 123, 'something');

bob.expect.greet.called.withMatch(/^The inspiration for this was/);

when the arg is not a primitive object

var bob = deride.stub(['greet']);
bob.greet('The inspiration for this was that my colleague was having a');
bob.greet({a: 123, b: { a: {'talula'}}, 123, 'something');

bob.expect.greet.called.withMatch(/^talula/gi);

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.