如何测试要单独一起使用的方法?

使用这个类:

var Observer = function Observer() {
    this._events = {};
};
Observer.prototype.on = function(k, v) {
    (this._events[k] = this._events[k] || []).push(v);
};
Observer.prototype.off = function(k, v) {
    var hs;
    var i;
    var l;
    if (!k) {
        this._events = {};
        return;
    }
    if (!v) {
        if (typeof this._events[k] !== 'undefined') {
            this._events[k] = [];
        }
        return;
    }
    hs = this._events[k];
    i = 0;
    l = hs.length;
    while(i < l) {
        if (hs[i] === v) {
            hs.splice(i);
        }
        i++;
    }
};
Observer.prototype.emit = function(k) {
    var hs = this._events[k];
    var args;
    var i;
    var l;
    if (hs) {
        args = [].splice.call(arguments, 1);
        i = 0;
        l = hs.length;
        while(i < l) {
            hs[i].apply(this, args);
            i++;
        }
    }
};
if (typeof exports !== 'undefined') {
    exports.Observer = Observer;
}

和这个测试代码:

var assert = require('assert');
var Observer = require('../../public/lib/Observer').Observer;
describe('Observer', function() {
    beforeEach(function(done) {
        this.instance = new Observer();
        done();
    });
    describe('#on', function() {
        describe('with an event and handler', function() {
            it('should call a callback', function(done) {
                var expected = 0;
                this.instance.on('a', function(actual) {
                    assert.equal(expected, actual);
                    done();
                });
                this.instance.emit('a', expected);
            });
        });
    });
    describe('#off', function() {
        describe('with an event and a handler', function() {
            it('should not call the callback', function(done) {
                var expected = false;
                var actual = false;
                var f = function() {
                    actual = true;
                };
                this.instance.on('a', f);
                this.instance.off('a', f);
                this.instance.emit('a');
                assert.equal(expected, actual);
                done()
            });
        });
        describe('with an event', function() {
            it('should not call the callback', function(done) {
                var expected = false;
                var actual = false;
                var f = function() {
                    actual = true;
                };
                this.instance.on('a', f);
                this.instance.off('a');
                this.instance.emit('a');
                assert.equal(expected, actual);
                done()
            });
        });
        describe('without arguments', function() {
            it('should not call the callback', function(done) {
                var expected = false;
                var actual = false;
                var f = function() {
                    actual = true;
                };
                this.instance.on('a', f);
                this.instance.off('a');
                this.instance.emit('a');
                assert.equal(expected, actual);
                done()
            });
        });
    });
    describe('#emit', function() {
        describe('with an event and variable arguments', function() {
            // I've already used this method in the other tests, so it must work in
            // order for them to pass. But that's not isolated testing, help :(..
        });
    });
});

运行这些测试(使用mocha)将通过所有测试，但是它们一起测试。

1. 这是测试这段代码的正确方法，使用所有的方法，在一个流程(s) ?

2. 如何单独测试这些方法?

   2.1。我不能看到我正在测试的结构的内部，因为我只是在测试实现，而不是接口。

   2.2。那么，.on(ev, fn)成功的标准是什么呢?