Test Cases for the Code

[C# Programming]

Hello All ,

I have developed my project . Now i want to Automate Test Framework . Ideally we should write Test cases as sooner as we writ the code .

But now i have develeoped all my Layers UI,BLL, DAL.

Now my question is In what order i should write the test cases I mean first i should for the dal then bll and then UI .

Or from top to bottom like UI--->BLL---->DAL

which approcah will be better Suggest .

Any pointers to above will be higly helpful to me

Regards,
Phani