No possible to mark default vader temp test file as modified

[mboughaba]

Given the vader test below, if found out that it is not possible to mark the vader temporary test file as modified.

Given (whatever):
  Bear claw gummi bears brownie cake. Sesame snaps cotton candy powder macaroon.              
  
Do (Mark file as modified):
  :let &mod = 1\<CR>
  :let &ro = 0\<CR>

Then (whatever):
  Log 'modified: ' . &mod
  Log 'readonly: ' . &ro

Expect (whatever):
  Bear claw gummi bears brownie cake. Sesame snaps cotton candy powder macaroon.

results will be:

  modified: 0
  readonly: 0

Any idea how to work around that?
It this case [Given/Do/Then/Expect] does Vader create a temp file behind the scene?