I am trying to have a variable be decremented and that result be used as
the BTFSC test bit

For example

movlw    H'07'
movwf    TestBit
decf        TestBit, 1
btfsc       PORTB, TestBit

Is this possible,  I tried using indirect referencing like

movlw    TestBit
movwf    FSR
btfsc       PORTB, INDF

but that will not work. Any suggestions.
Thanks