だいたいあってたらOKになるテスト

custom-should.js

var should = require("should");
var i = require("util").inspect;

var NEARLY_PRECISION = 1/1000000;

if (! Object.getOwnPropertyDescriptor(should.Assertion.prototype, "nearly") ) {
    Object.defineProperty(should.Assertion.prototype, "nearly", {
        get: function() {
            this.nearlyflag = true
            return this;
        }
    });
}

should.Assertion.prototype.equal = function(val, desc) {
    var actual = this.nearlyflag ?
        Math.abs(val.valueOf() - this.obj) < NEARLY_PRECISION :
        val.valueOf() === this.obj;
    this.nearlyflag = false;
    
    this.assert(
        actual
        , 'expected ' + this.inspect + ' to equal ' + i(val) + (desc ? " | " + desc : "")
        , 'expected ' + this.inspect + ' to not equal ' + i(val) + (desc ? " | " + desc : "")
        , val);
    
    return this;
};

usage.coffee

describe "usage", ->

    # これだとテストが通らない
    # AssertionError: expected 1.4142135623730951 to equal 1.41421356
    it "sqrt(2) is 1.41421356", ->
        Math.sqrt(2).should.equal 1.41421356


    # こっちは通る
    it "sqrt(2) is nearly 1.41421356", ->
        Math.sqrt(2).should.nearly.equal 1.41421356