how can I capturescreen and put the image in my folder

I want to capture screen and save the image in my defined folder. so I do like this:

set imageFolder to my folder’s folder & “Output/”
set imageName to imageFolder & “test.tiff”
captureScreen imageName

But I always get this error:

“image not saved: unable to determine save directory”
Is any place for me to configure the path that I want to use in eggplant?