(function(global, module) {
    var exports = module.exports;

    /**
   * Exports.
   */

    module.exports = expect;
    expect.Assertion = Assertion;

    /**
   * Exports version.
   */

    expect.version = '0.3.1';

    /**
   * Possible assertion flags.
   */

    var flags = {
        not: ['to', 'be', 'have', 'include', 'only'],
        to: ['be', 'have', 'include', 'only', 'not'],
        only: ['have'],
        have: ['own'],
        be: ['an']
    };

    function expect(obj) {
        return new Assertion(obj);
    }

    /**
   * Constructor
   *
   * @api private
   */

    function Assertion(obj, flag, parent) {
        this.obj = obj;
        this.flags = {};

        if (undefined != parent) {
            this.flags[flag] = true;

            for (var i in parent.flags) {
                if (parent.flags.hasOwnProperty(i)) {
                    this.flags[i] = true;
                }
            }
        }

        var $flags = flag ? flags[flag] : keys(flags),
            self = this;

        if ($flags) {
            for (var i = 0, l = $flags.length; i < l; i++) {
                // avoid recursion
                if (this.flags[$flags[i]]) continue;

                var name = $flags[i],
                    assertion = new Assertion(this.obj, name, this);

                if ('function' == typeof Assertion.prototype[name]) {
                    // clone the function, make sure we dont touch the prot reference
                    var old = this[name];
                    this[name] = function() {
                        return old.apply(self, arguments);
                    };

                    for (var fn in Assertion.prototype) {
                        if (Assertion.prototype.hasOwnProperty(fn) && fn != name) {
                            this[name][fn] = bind(assertion[fn], assertion);
                        }
                    }
                } else {
                    this[name] = assertion;
                }
            }
        }
    }

    /**
   * Performs an assertion
   *
   * @api private
   */

    Assertion.prototype.assert = function(truth, msg, error, expected) {
        var msg = this.flags.not ? error : msg,
            ok = this.flags.not ? !truth : truth,
            err;

        if (!ok) {
            err = new Error(msg.call(this));
            if (arguments.length > 3) {
                err.actual = this.obj;
                err.expected = expected;
                err.showDiff = true;
            }
            throw err;
        }

        this.and = new Assertion(this.obj);
    };

    /**
   * Check if the value is truthy
   *
   * @api public
   */

    Assertion.prototype.ok = function() {
        this.assert(
            !!this.obj,
            function() {
                return 'expected ' + i(this.obj) + ' to be truthy';
            },
            function() {
                return 'expected ' + i(this.obj) + ' to be falsy';
            }
        );
    };

    /**
   * Creates an anonymous function which calls fn with arguments.
   *
   * @api public
   */

    Assertion.prototype.withArgs = function() {
        expect(this.obj).to.be.a('function');
        var fn = this.obj;
        var args = Array.prototype.slice.call(arguments);
        return expect(function() {
            fn.apply(null, args);
        });
    };

    /**
   * Assert that the function throws.
   *
   * @param {Function|RegExp} callback, or regexp to match error string against
   * @api public
   */

    Assertion.prototype.throwError = Assertion.prototype.throwException = function(fn) {
        expect(this.obj).to.be.a('function');

        var thrown = false,
            not = this.flags.not;

        try {
            this.obj();
        } catch (e) {
            if (isRegExp(fn)) {
                var subject = 'string' == typeof e ? e : e.message;
                if (not) {
                    expect(subject).to.not.match(fn);
                } else {
                    expect(subject).to.match(fn);
                }
            } else if ('function' == typeof fn) {
                fn(e);
            }
            thrown = true;
        }

        if (isRegExp(fn) && not) {
            // in the presence of a matcher, ensure the `not` only applies to
            // the matching.
            this.flags.not = false;
        }

        var name = this.obj.name || 'fn';
        this.assert(
            thrown,
            function() {
                return 'expected ' + name + ' to throw an exception';
            },
            function() {
                return 'expected ' + name + ' not to throw an exception';
            }
        );
    };

    /**
   * Checks if the array is empty.
   *
   * @api public
   */

    Assertion.prototype.empty = function() {
        var expectation;

        if ('object' == typeof this.obj && null !== this.obj && !isArray(this.obj)) {
            if ('number' == typeof this.obj.length) {
                expectation = !this.obj.length;
            } else {
                expectation = !keys(this.obj).length;
            }
        } else {
            if ('string' != typeof this.obj) {
                expect(this.obj).to.be.an('object');
            }

            expect(this.obj).to.have.property('length');
            expectation = !this.obj.length;
        }

        this.assert(
            expectation,
            function() {
                return 'expected ' + i(this.obj) + ' to be empty';
            },
            function() {
                return 'expected ' + i(this.obj) + ' to not be empty';
            }
        );
        return this;
    };

    /**
   * Checks if the obj exactly equals another.
   *
   * @api public
   */

    Assertion.prototype.be = Assertion.prototype.equal = function(obj) {
        this.assert(
            obj === this.obj,
            function() {
                return 'expected ' + i(this.obj) + ' to equal ' + i(obj);
            },
            function() {
                return 'expected ' + i(this.obj) + ' to not equal ' + i(obj);
            }
        );
        return this;
    };

    /**
   * Checks if the obj sortof equals another.
   *
   * @api public
   */

    Assertion.prototype.eql = function(obj) {
        this.assert(
            expect.eql(this.obj, obj),
            function() {
                return 'expected ' + i(this.obj) + ' to sort of equal ' + i(obj);
            },
            function() {
                return 'expected ' + i(this.obj) + ' to sort of not equal ' + i(obj);
            },
            obj
        );
        return this;
    };

    /**
   * Assert within start to finish (inclusive).
   *
   * @param {Number} start
   * @param {Number} finish
   * @api public
   */

    Assertion.prototype.within = function(start, finish) {
        var range = start + '..' + finish;
        this.assert(
            this.obj >= start && this.obj <= finish,
            function() {
                return 'expected ' + i(this.obj) + ' to be within ' + range;
            },
            function() {
                return 'expected ' + i(this.obj) + ' to not be within ' + range;
            }
        );
        return this;
    };

    /**
   * Assert typeof / instance of
   *
   * @api public
   */

    Assertion.prototype.a = Assertion.prototype.an = function(type) {
        if ('string' == typeof type) {
            // proper english in error msg
            var n = /^[aeiou]/.test(type) ? 'n' : '';

            // typeof with support for 'array'
            this.assert(
                'array' == type
                    ? isArray(this.obj)
                    : 'regexp' == type
                      ? isRegExp(this.obj)
                      : 'object' == type
                        ? 'object' == typeof this.obj && null !== this.obj
                        : type == typeof this.obj,
                function() {
                    return 'expected ' + i(this.obj) + ' to be a' + n + ' ' + type;
                },
                function() {
                    return 'expected ' + i(this.obj) + ' not to be a' + n + ' ' + type;
                }
            );
        } else {
            // instanceof
            var name = type.name || 'supplied constructor';
            this.assert(
                this.obj instanceof type,
                function() {
                    return 'expected ' + i(this.obj) + ' to be an instance of ' + name;
                },
                function() {
                    return 'expected ' + i(this.obj) + ' not to be an instance of ' + name;
                }
            );
        }

        return this;
    };

    /**
   * Assert numeric value above _n_.
   *
   * @param {Number} n
   * @api public
   */

    Assertion.prototype.greaterThan = Assertion.prototype.above = function(n) {
        this.assert(
            this.obj > n,
            function() {
                return 'expected ' + i(this.obj) + ' to be above ' + n;
            },
            function() {
                return 'expected ' + i(this.obj) + ' to be below ' + n;
            }
        );
        return this;
    };

    /**
   * Assert numeric value below _n_.
   *
   * @param {Number} n
   * @api public
   */

    Assertion.prototype.lessThan = Assertion.prototype.below = function(n) {
        this.assert(
            this.obj < n,
            function() {
                return 'expected ' + i(this.obj) + ' to be below ' + n;
            },
            function() {
                return 'expected ' + i(this.obj) + ' to be above ' + n;
            }
        );
        return this;
    };

    /**
   * Assert string value matches _regexp_.
   *
   * @param {RegExp} regexp
   * @api public
   */

    Assertion.prototype.match = function(regexp) {
        this.assert(
            regexp.exec(this.obj),
            function() {
                return 'expected ' + i(this.obj) + ' to match ' + regexp;
            },
            function() {
                return 'expected ' + i(this.obj) + ' not to match ' + regexp;
            }
        );
        return this;
    };

    /**
   * Assert property "length" exists and has value of _n_.
   *
   * @param {Number} n
   * @api public
   */

    Assertion.prototype.length = function(n) {
        expect(this.obj).to.have.property('length');
        var len = this.obj.length;
        this.assert(
            n == len,
            function() {
                return 'expected ' + i(this.obj) + ' to have a length of ' + n + ' but got ' + len;
            },
            function() {
                return 'expected ' + i(this.obj) + ' to not have a length of ' + len;
            }
        );
        return this;
    };

    /**
   * Assert property _name_ exists, with optional _val_.
   *
   * @param {String} name
   * @param {Mixed} val
   * @api public
   */

    Assertion.prototype.property = function(name, val) {
        if (this.flags.own) {
            this.assert(
                Object.prototype.hasOwnProperty.call(this.obj, name),
                function() {
                    return 'expected ' + i(this.obj) + ' to have own property ' + i(name);
                },
                function() {
                    return 'expected ' + i(this.obj) + ' to not have own property ' + i(name);
                }
            );
            return this;
        }

        if (this.flags.not && undefined !== val) {
            if (undefined === this.obj[name]) {
                throw new Error(i(this.obj) + ' has no property ' + i(name));
            }
        } else {
            var hasProp;
            try {
                hasProp = name in this.obj;
            } catch (e) {
                hasProp = undefined !== this.obj[name];
            }

            this.assert(
                hasProp,
                function() {
                    return 'expected ' + i(this.obj) + ' to have a property ' + i(name);
                },
                function() {
                    return 'expected ' + i(this.obj) + ' to not have a property ' + i(name);
                }
            );
        }

        if (undefined !== val) {
            this.assert(
                val === this.obj[name],
                function() {
                    return (
                        'expected ' +
                        i(this.obj) +
                        ' to have a property ' +
                        i(name) +
                        ' of ' +
                        i(val) +
                        ', but got ' +
                        i(this.obj[name])
                    );
                },
                function() {
                    return (
                        'expected ' +
                        i(this.obj) +
                        ' to not have a property ' +
                        i(name) +
                        ' of ' +
                        i(val)
                    );
                }
            );
        }

        this.obj = this.obj[name];
        return this;
    };

    /**
   * Assert that the array contains _obj_ or string contains _obj_.
   *
   * @param {Mixed} obj|string
   * @api public
   */

    Assertion.prototype.string = Assertion.prototype.contain = function(obj) {
        if ('string' == typeof this.obj) {
            this.assert(
                ~this.obj.indexOf(obj),
                function() {
                    return 'expected ' + i(this.obj) + ' to contain ' + i(obj);
                },
                function() {
                    return 'expected ' + i(this.obj) + ' to not contain ' + i(obj);
                }
            );
        } else {
            this.assert(
                ~indexOf(this.obj, obj),
                function() {
                    return 'expected ' + i(this.obj) + ' to contain ' + i(obj);
                },
                function() {
                    return 'expected ' + i(this.obj) + ' to not contain ' + i(obj);
                }
            );
        }
        return this;
    };

    /**
   * Assert exact keys or inclusion of keys by using
   * the `.own` modifier.
   *
   * @param {Array|String ...} keys
   * @api public
   */

    Assertion.prototype.key = Assertion.prototype.keys = function($keys) {
        var str,
            ok = true;

        $keys = isArray($keys) ? $keys : Array.prototype.slice.call(arguments);

        if (!$keys.length) throw new Error('keys required');

        var actual = keys(this.obj),
            len = $keys.length;

        // Inclusion
        ok = every($keys, function(key) {
            return ~indexOf(actual, key);
        });

        // Strict
        if (!this.flags.not && this.flags.only) {
            ok = ok && $keys.length == actual.length;
        }

        // Key string
        if (len > 1) {
            $keys = map($keys, function(key) {
                return i(key);
            });
            var last = $keys.pop();
            str = $keys.join(', ') + ', and ' + last;
        } else {
            str = i($keys[0]);
        }

        // Form
        str = (len > 1 ? 'keys ' : 'key ') + str;

        // Have / include
        str = (!this.flags.only ? 'include ' : 'only have ') + str;

        // Assertion
        this.assert(
            ok,
            function() {
                return 'expected ' + i(this.obj) + ' to ' + str;
            },
            function() {
                return 'expected ' + i(this.obj) + ' to not ' + str;
            }
        );

        return this;
    };

    /**
   * Assert a failure.
   *
   * @param {String ...} custom message
   * @api public
   */
    Assertion.prototype.fail = function(msg) {
        var error = function() {
            return msg || 'explicit failure';
        };
        this.assert(false, error, error);
        return this;
    };

    /**
   * Function bind implementation.
   */

    function bind(fn, scope) {
        return function() {
            return fn.apply(scope, arguments);
        };
    }

    /**
   * Array every compatibility
   *
   * @see bit.ly/5Fq1N2
   * @api public
   */

    function every(arr, fn, thisObj) {
        var scope = thisObj || global;
        for (var i = 0, j = arr.length; i < j; ++i) {
            if (!fn.call(scope, arr[i], i, arr)) {
                return false;
            }
        }
        return true;
    }

    /**
   * Array indexOf compatibility.
   *
   * @see bit.ly/a5Dxa2
   * @api public
   */

    function indexOf(arr, o, i) {
        if (Array.prototype.indexOf) {
            return Array.prototype.indexOf.call(arr, o, i);
        }

        if (arr.length === undefined) {
            return -1;
        }

        for (
            var j = arr.length, i = i < 0 ? (i + j < 0 ? 0 : i + j) : i || 0;
            i < j && arr[i] !== o;
            i++
        );

        return j <= i ? -1 : i;
    }

    // https://gist.github.com/1044128/
    var getOuterHTML = function(element) {
        if ('outerHTML' in element) return element.outerHTML;
        var ns = 'http://www.w3.org/1999/xhtml';
        var container = document.createElementNS(ns, '_');
        var xmlSerializer = new XMLSerializer();
        var html;
        if (document.xmlVersion) {
            return xmlSerializer.serializeToString(element);
        } else {
            container.appendChild(element.cloneNode(false));
            html = container.innerHTML.replace('><', '>' + element.innerHTML + '<');
            container.innerHTML = '';
            return html;
        }
    };

    // Returns true if object is a DOM element.
    var isDOMElement = function(object) {
        if (typeof HTMLElement === 'object') {
            return object instanceof HTMLElement;
        } else {
            return (
                object &&
                typeof object === 'object' &&
                object.nodeType === 1 &&
                typeof object.nodeName === 'string'
            );
        }
    };

    /**
   * Inspects an object.
   *
   * @see taken from node.js `util` module (copyright Joyent, MIT license)
   * @api private
   */

    function i(obj, showHidden, depth) {
        var seen = [];

        function stylize(str) {
            return str;
        }

        function format(value, recurseTimes) {
            // Provide a hook for user-specified inspect functions.
            // Check that value is an object with an inspect function on it
            if (
                value &&
                typeof value.inspect === 'function' &&
                // Filter out the util module, it's inspect function is special
                value !== exports &&
                // Also filter out any prototype objects using the circular check.
                !(value.constructor && value.constructor.prototype === value)
            ) {
                return value.inspect(recurseTimes);
            }

            // Primitive types cannot have properties
            switch (typeof value) {
                case 'undefined':
                    return stylize('undefined', 'undefined');

                case 'string':
                    var simple =
                        "'" +
                        json
                            .stringify(value)
                            .replace(/^"|"$/g, '')
                            .replace(/'/g, "\\'")
                            .replace(/\\"/g, '"') +
                        "'";
                    return stylize(simple, 'string');

                case 'number':
                    return stylize('' + value, 'number');

                case 'boolean':
                    return stylize('' + value, 'boolean');
            }
            // For some reason typeof null is "object", so special case here.
            if (value === null) {
                return stylize('null', 'null');
            }

            if (isDOMElement(value)) {
                return getOuterHTML(value);
            }

            // Look up the keys of the object.
            var visible_keys = keys(value);
            var $keys = showHidden ? Object.getOwnPropertyNames(value) : visible_keys;

            // Functions without properties can be shortcutted.
            if (typeof value === 'function' && $keys.length === 0) {
                if (isRegExp(value)) {
                    return stylize('' + value, 'regexp');
                } else {
                    var name = value.name ? ': ' + value.name : '';
                    return stylize('[Function' + name + ']', 'special');
                }
            }

            // Dates without properties can be shortcutted
            if (isDate(value) && $keys.length === 0) {
                return stylize(value.toUTCString(), 'date');
            }

            // Error objects can be shortcutted
            if (value instanceof Error) {
                return stylize('[' + value.toString() + ']', 'Error');
            }

            var base, type, braces;
            // Determine the object type
            if (isArray(value)) {
                type = 'Array';
                braces = ['[', ']'];
            } else {
                type = 'Object';
                braces = ['{', '}'];
            }

            // Make functions say that they are functions
            if (typeof value === 'function') {
                var n = value.name ? ': ' + value.name : '';
                base = isRegExp(value) ? ' ' + value : ' [Function' + n + ']';
            } else {
                base = '';
            }

            // Make dates with properties first say the date
            if (isDate(value)) {
                base = ' ' + value.toUTCString();
            }

            if ($keys.length === 0) {
                return braces[0] + base + braces[1];
            }

            if (recurseTimes < 0) {
                if (isRegExp(value)) {
                    return stylize('' + value, 'regexp');
                } else {
                    return stylize('[Object]', 'special');
                }
            }

            seen.push(value);

            var output = map($keys, function(key) {
                var name, str;
                if (value.__lookupGetter__) {
                    if (value.__lookupGetter__(key)) {
                        if (value.__lookupSetter__(key)) {
                            str = stylize('[Getter/Setter]', 'special');
                        } else {
                            str = stylize('[Getter]', 'special');
                        }
                    } else {
                        if (value.__lookupSetter__(key)) {
                            str = stylize('[Setter]', 'special');
                        }
                    }
                }
                if (indexOf(visible_keys, key) < 0) {
                    name = '[' + key + ']';
                }
                if (!str) {
                    if (indexOf(seen, value[key]) < 0) {
                        if (recurseTimes === null) {
                            str = format(value[key]);
                        } else {
                            str = format(value[key], recurseTimes - 1);
                        }
                        if (str.indexOf('\n') > -1) {
                            if (isArray(value)) {
                                str = map(str.split('\n'), function(line) {
                                    return '  ' + line;
                                })
                                    .join('\n')
                                    .substr(2);
                            } else {
                                str =
                                    '\n' +
                                    map(str.split('\n'), function(line) {
                                        return '   ' + line;
                                    }).join('\n');
                            }
                        }
                    } else {
                        str = stylize('[Circular]', 'special');
                    }
                }
                if (typeof name === 'undefined') {
                    if (type === 'Array' && key.match(/^\d+$/)) {
                        return str;
                    }
                    name = json.stringify('' + key);
                    if (name.match(/^"([a-zA-Z_][a-zA-Z_0-9]*)"$/)) {
                        name = name.substr(1, name.length - 2);
                        name = stylize(name, 'name');
                    } else {
                        name = name
                            .replace(/'/g, "\\'")
                            .replace(/\\"/g, '"')
                            .replace(/(^"|"$)/g, "'");
                        name = stylize(name, 'string');
                    }
                }

                return name + ': ' + str;
            });

            seen.pop();

            var numLinesEst = 0;
            var length = reduce(
                output,
                function(prev, cur) {
                    numLinesEst++;
                    if (indexOf(cur, '\n') >= 0) numLinesEst++;
                    return prev + cur.length + 1;
                },
                0
            );

            if (length > 50) {
                output =
                    braces[0] +
                    (base === '' ? '' : base + '\n ') +
                    ' ' +
                    output.join(',\n  ') +
                    ' ' +
                    braces[1];
            } else {
                output = braces[0] + base + ' ' + output.join(', ') + ' ' + braces[1];
            }

            return output;
        }
        return format(obj, typeof depth === 'undefined' ? 2 : depth);
    }

    expect.stringify = i;

    function isArray(ar) {
        return Object.prototype.toString.call(ar) === '[object Array]';
    }

    function isRegExp(re) {
        var s;
        try {
            s = '' + re;
        } catch (e) {
            return false;
        }

        return (
            re instanceof RegExp || // easy case
            // duck-type for context-switching evalcx case
            (typeof re === 'function' &&
                re.constructor.name === 'RegExp' &&
                re.compile &&
                re.test &&
                re.exec &&
                s.match(/^\/.*\/[gim]{0,3}$/))
        );
    }

    function isDate(d) {
        return d instanceof Date;
    }

    function keys(obj) {
        if (Object.keys) {
            return Object.keys(obj);
        }

        var keys = [];

        for (var i in obj) {
            if (Object.prototype.hasOwnProperty.call(obj, i)) {
                keys.push(i);
            }
        }

        return keys;
    }

    function map(arr, mapper, that) {
        if (Array.prototype.map) {
            return Array.prototype.map.call(arr, mapper, that);
        }

        var other = new Array(arr.length);

        for (var i = 0, n = arr.length; i < n; i++)
            if (i in arr) other[i] = mapper.call(that, arr[i], i, arr);

        return other;
    }

    function reduce(arr, fun) {
        if (Array.prototype.reduce) {
            return Array.prototype.reduce.apply(arr, Array.prototype.slice.call(arguments, 1));
        }

        var len = +this.length;

        if (typeof fun !== 'function') throw new TypeError();

        // no value to return if no initial value and an empty array
        if (len === 0 && arguments.length === 1) throw new TypeError();

        var i = 0;
        if (arguments.length >= 2) {
            var rv = arguments[1];
        } else {
            do {
                if (i in this) {
                    rv = this[i++];
                    break;
                }

                // if array contains no values, no initial value to return
                if (++i >= len) throw new TypeError();
            } while (true);
        }

        for (; i < len; i++) {
            if (i in this) rv = fun.call(null, rv, this[i], i, this);
        }

        return rv;
    }

    /**
   * Asserts deep equality
   *
   * @see taken from node.js `assert` module (copyright Joyent, MIT license)
   * @api private
   */

    expect.eql = function eql(actual, expected) {
        // 7.1. All identical values are equivalent, as determined by ===.
        if (actual === expected) {
            return true;
        } else if (
            'undefined' != typeof Buffer &&
            Buffer.isBuffer(actual) &&
            Buffer.isBuffer(expected)
        ) {
            if (actual.length != expected.length) return false;

            for (var i = 0; i < actual.length; i++) {
                if (actual[i] !== expected[i]) return false;
            }

            return true;

            // 7.2. If the expected value is a Date object, the actual value is
            // equivalent if it is also a Date object that refers to the same time.
        } else if (actual instanceof Date && expected instanceof Date) {
            return actual.getTime() === expected.getTime();

            // 7.3. Other pairs that do not both pass typeof value == "object",
            // equivalence is determined by ==.
        } else if (typeof actual != 'object' && typeof expected != 'object') {
            return actual == expected;
            // If both are regular expression use the special `regExpEquiv` method
            // to determine equivalence.
        } else if (isRegExp(actual) && isRegExp(expected)) {
            return regExpEquiv(actual, expected);
            // 7.4. For all other Object pairs, including Array objects, equivalence is
            // determined by having the same number of owned properties (as verified
            // with Object.prototype.hasOwnProperty.call), the same set of keys
            // (although not necessarily the same order), equivalent values for every
            // corresponding key, and an identical "prototype" property. Note: this
            // accounts for both named and indexed properties on Arrays.
        } else {
            return objEquiv(actual, expected);
        }
    };

    function isUndefinedOrNull(value) {
        return value === null || value === undefined;
    }

    function isArguments(object) {
        return Object.prototype.toString.call(object) == '[object Arguments]';
    }

    function regExpEquiv(a, b) {
        return (
            a.source === b.source &&
            a.global === b.global &&
            a.ignoreCase === b.ignoreCase &&
            a.multiline === b.multiline
        );
    }

    function objEquiv(a, b) {
        if (isUndefinedOrNull(a) || isUndefinedOrNull(b)) return false;
        // an identical "prototype" property.
        if (a.prototype !== b.prototype) return false;
        //~~~I've managed to break Object.keys through screwy arguments passing.
        //   Converting to array solves the problem.
        if (isArguments(a)) {
            if (!isArguments(b)) {
                return false;
            }
            a = pSlice.call(a);
            b = pSlice.call(b);
            return expect.eql(a, b);
        }
        try {
            var ka = keys(a),
                kb = keys(b),
                key,
                i;
        } catch (e) {
            //happens when one is a string literal and the other isn't
            return false;
        }
        // having the same number of owned properties (keys incorporates hasOwnProperty)
        if (ka.length != kb.length) return false;
        //the same set of keys (although not necessarily the same order),
        ka.sort();
        kb.sort();
        //~~~cheap key test
        for (i = ka.length - 1; i >= 0; i--) {
            if (ka[i] != kb[i]) return false;
        }
        //equivalent values for every corresponding key, and
        //~~~possibly expensive deep test
        for (i = ka.length - 1; i >= 0; i--) {
            key = ka[i];
            if (!expect.eql(a[key], b[key])) return false;
        }
        return true;
    }

    var json = (function() {
        'use strict';

        if ('object' == typeof JSON && JSON.parse && JSON.stringify) {
            return {
                parse: nativeJSON.parse,
                stringify: nativeJSON.stringify
            };
        }

        var JSON = {};

        function f(n) {
            // Format integers to have at least two digits.
            return n < 10 ? '0' + n : n;
        }

        function date(d, key) {
            return isFinite(d.valueOf())
                ? d.getUTCFullYear() +
                  '-' +
                  f(d.getUTCMonth() + 1) +
                  '-' +
                  f(d.getUTCDate()) +
                  'T' +
                  f(d.getUTCHours()) +
                  ':' +
                  f(d.getUTCMinutes()) +
                  ':' +
                  f(d.getUTCSeconds()) +
                  'Z'
                : null;
        }

        var cx = /[\u0000\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,
            escapable = /[\\\"\x00-\x1f\x7f-\x9f\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,
            gap,
            indent,
            meta = {
                // table of character substitutions
                '\b': '\\b',
                '\t': '\\t',
                '\n': '\\n',
                '\f': '\\f',
                '\r': '\\r',
                '"': '\\"',
                '\\': '\\\\'
            },
            rep;

        function quote(string) {
            // If the string contains no control characters, no quote characters, and no
            // backslash characters, then we can safely slap some quotes around it.
            // Otherwise we must also replace the offending characters with safe escape
            // sequences.

            escapable.lastIndex = 0;
            return escapable.test(string)
                ? '"' +
                  string.replace(escapable, function(a) {
                      var c = meta[a];
                      return typeof c === 'string'
                          ? c
                          : '\\u' + ('0000' + a.charCodeAt(0).toString(16)).slice(-4);
                  }) +
                  '"'
                : '"' + string + '"';
        }

        function str(key, holder) {
            // Produce a string from holder[key].

            var i, // The loop counter.
                k, // The member key.
                v, // The member value.
                length,
                mind = gap,
                partial,
                value = holder[key];

            // If the value has a toJSON method, call it to obtain a replacement value.

            if (value instanceof Date) {
                value = date(key);
            }

            // If we were called with a replacer function, then call the replacer to
            // obtain a replacement value.

            if (typeof rep === 'function') {
                value = rep.call(holder, key, value);
            }

            // What happens next depends on the value's type.

            switch (typeof value) {
                case 'string':
                    return quote(value);

                case 'number':
                    // JSON numbers must be finite. Encode non-finite numbers as null.

                    return isFinite(value) ? String(value) : 'null';

                case 'boolean':
                case 'null':
                    // If the value is a boolean or null, convert it to a string. Note:
                    // typeof null does not produce 'null'. The case is included here in
                    // the remote chance that this gets fixed someday.

                    return String(value);

                // If the type is 'object', we might be dealing with an object or an array or
                // null.

                case 'object':
                    // Due to a specification blunder in ECMAScript, typeof null is 'object',
                    // so watch out for that case.

                    if (!value) {
                        return 'null';
                    }

                    // Make an array to hold the partial results of stringifying this object value.

                    gap += indent;
                    partial = [];

                    // Is the value an array?

                    if (Object.prototype.toString.apply(value) === '[object Array]') {
                        // The value is an array. Stringify every element. Use null as a placeholder
                        // for non-JSON values.

                        length = value.length;
                        for (i = 0; i < length; i += 1) {
                            partial[i] = str(i, value) || 'null';
                        }

                        // Join all of the elements together, separated with commas, and wrap them in
                        // brackets.

                        v =
                            partial.length === 0
                                ? '[]'
                                : gap
                                  ? '[\n' + gap + partial.join(',\n' + gap) + '\n' + mind + ']'
                                  : '[' + partial.join(',') + ']';
                        gap = mind;
                        return v;
                    }

                    // If the replacer is an array, use it to select the members to be stringified.

                    if (rep && typeof rep === 'object') {
                        length = rep.length;
                        for (i = 0; i < length; i += 1) {
                            if (typeof rep[i] === 'string') {
                                k = rep[i];
                                v = str(k, value);
                                if (v) {
                                    partial.push(quote(k) + (gap ? ': ' : ':') + v);
                                }
                            }
                        }
                    } else {
                        // Otherwise, iterate through all of the keys in the object.

                        for (k in value) {
                            if (Object.prototype.hasOwnProperty.call(value, k)) {
                                v = str(k, value);
                                if (v) {
                                    partial.push(quote(k) + (gap ? ': ' : ':') + v);
                                }
                            }
                        }
                    }

                    // Join all of the member texts together, separated with commas,
                    // and wrap them in braces.

                    v =
                        partial.length === 0
                            ? '{}'
                            : gap
                              ? '{\n' + gap + partial.join(',\n' + gap) + '\n' + mind + '}'
                              : '{' + partial.join(',') + '}';
                    gap = mind;
                    return v;
            }
        }

        // If the JSON object does not yet have a stringify method, give it one.

        JSON.stringify = function(value, replacer, space) {
            // The stringify method takes a value and an optional replacer, and an optional
            // space parameter, and returns a JSON text. The replacer can be a function
            // that can replace values, or an array of strings that will select the keys.
            // A default replacer method can be provided. Use of the space parameter can
            // produce text that is more easily readable.

            var i;
            gap = '';
            indent = '';

            // If the space parameter is a number, make an indent string containing that
            // many spaces.

            if (typeof space === 'number') {
                for (i = 0; i < space; i += 1) {
                    indent += ' ';
                }

                // If the space parameter is a string, it will be used as the indent string.
            } else if (typeof space === 'string') {
                indent = space;
            }

            // If there is a replacer, it must be a function or an array.
            // Otherwise, throw an error.

            rep = replacer;
            if (
                replacer &&
                typeof replacer !== 'function' &&
                (typeof replacer !== 'object' || typeof replacer.length !== 'number')
            ) {
                throw new Error('JSON.stringify');
            }

            // Make a fake root object containing our value under the key of ''.
            // Return the result of stringifying the value.

            return str('', {'': value});
        };

        // If the JSON object does not yet have a parse method, give it one.

        JSON.parse = function(text, reviver) {
            // The parse method takes a text and an optional reviver function, and returns
            // a JavaScript value if the text is a valid JSON text.

            var j;

            function walk(holder, key) {
                // The walk method is used to recursively walk the resulting structure so
                // that modifications can be made.

                var k,
                    v,
                    value = holder[key];
                if (value && typeof value === 'object') {
                    for (k in value) {
                        if (Object.prototype.hasOwnProperty.call(value, k)) {
                            v = walk(value, k);
                            if (v !== undefined) {
                                value[k] = v;
                            } else {
                                delete value[k];
                            }
                        }
                    }
                }
                return reviver.call(holder, key, value);
            }

            // Parsing happens in four stages. In the first stage, we replace certain
            // Unicode characters with escape sequences. JavaScript handles many characters
            // incorrectly, either silently deleting them, or treating them as line endings.

            text = String(text);
            cx.lastIndex = 0;
            if (cx.test(text)) {
                text = text.replace(cx, function(a) {
                    return '\\u' + ('0000' + a.charCodeAt(0).toString(16)).slice(-4);
                });
            }

            // In the second stage, we run the text against regular expressions that look
            // for non-JSON patterns. We are especially concerned with '()' and 'new'
            // because they can cause invocation, and '=' because it can cause mutation.
            // But just to be safe, we want to reject all unexpected forms.

            // We split the second stage into 4 regexp operations in order to work around
            // crippling inefficiencies in IE's and Safari's regexp engines. First we
            // replace the JSON backslash pairs with '@' (a non-JSON character). Second, we
            // replace all simple value tokens with ']' characters. Third, we delete all
            // open brackets that follow a colon or comma or that begin the text. Finally,
            // we look to see that the remaining characters are only whitespace or ']' or
            // ',' or ':' or '{' or '}'. If that is so, then the text is safe for eval.

            if (
                /^[\],:{}\s]*$/.test(
                    text
                        .replace(/\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g, '@')
                        .replace(
                            /"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g,
                            ']'
                        )
                        .replace(/(?:^|:|,)(?:\s*\[)+/g, '')
                )
            ) {
                // In the third stage we use the eval function to compile the text into a
                // JavaScript structure. The '{' operator is subject to a syntactic ambiguity
                // in JavaScript: it can begin a block or an object literal. We wrap the text
                // in parens to eliminate the ambiguity.

                j = eval('(' + text + ')');

                // In the optional fourth stage, we recursively walk the new structure, passing
                // each name/value pair to a reviver function for possible transformation.

                return typeof reviver === 'function' ? walk({'': j}, '') : j;
            }

            // If the text is not JSON parseable, then a SyntaxError is thrown.

            throw new SyntaxError('JSON.parse');
        };

        return JSON;
    })();

    if ('undefined' != typeof window) {
        window.expect = module.exports;
    }
})(this, 'undefined' != typeof module ? module : {exports: {}});