任意精度JavaScript上的浮点数(Arbitrary precision Float numbers on JavaScript)

 在测试场景中去解决这个问题的一种方法是这样的： 
 
// at first you have to create the object
DB_Object__c dbObj = new DB_Object__c();
dbObj.Name = 'test';
dbObj.Setting = 'aSetting';
insert dbObj;

// then you'd call the vf page with the id query paramter
Test.setCurrentPageReference(Page.Demo);
ApexPages.currentPage().getParameters().put('id', dbObj.Id);
dbObj = [Select All, Fields, You, Need From DB_Object__c Where Id = :ApexPages.currentPage().getParamters().get('id')];

// then the StandardController & controller extension get initiated
ApexPages.StandardController sc = new ApexPages.StandardController(dbObj);
MyExtension myExt = new MyExtension(sc);
 
 现在你的问题为什么getParameters().get('id')失败？ 你可以启动一个没有记录ID的StandardController，它会给你一个新的记录，并且如果你使用默认的save PageReference，它会自动插入记录。 

One way to go about this in a test scenario would be something like this:
 
// at first you have to create the object
DB_Object__c dbObj = new DB_Object__c();
dbObj.Name = 'test';
dbObj.Setting = 'aSetting';
insert dbObj;

// then you'd call the vf page with the id query paramter
Test.setCurrentPageReference(Page.Demo);
ApexPages.currentPage().getParameters().put('id', dbObj.Id);
dbObj = [Select All, Fields, You, Need From DB_Object__c Where Id = :ApexPages.currentPage().getParamters().get('id')];

// then the StandardController & controller extension get initiated
ApexPages.StandardController sc = new ApexPages.StandardController(dbObj);
MyExtension myExt = new MyExtension(sc);
 
Now to your question why does getParameters().get('id') fail? You can initiate a StandardController without a record id which would give you a new record and automatically insert the record if you use the default save PageReference.