And it doesnt place rail bridges correclty.

The scenario level caused a non-recoverable error.
Please report this error to the scenario author.

Error while running event level::on_gui_click (ID 1)
__level__/control.lua:634: attempt to index local 'ent' (a nil value)
stack traceback:
    __level__/control.lua:634: in function 'ExtendLine'
    __level__/control.lua:457: in function 'StartBPTest'
    __level__/control.lua:433: in function 'StartTest'
    __level__/control.lua:126: in function <__level__/control.lua:118>

The blueprint I used is the Advanced Roundabout from https://forums.factorio.com/viewtopic.php?f=194&t=115929

ok rail bridges not placing right is a known issue with how it unghosts the blueprint (trying to unghost an elevated rail before you unghost its support doesnt work)

as for the blueprint in question, it appears to be detecting 12 external connections when clearly only 8 exist. ill look at it tomorrow morning

curiosity got the better of me, so i did not go to bed. it appears the issue in your case was that there were stray ground level rails hidden under the elevated rails in the middle. the tester saw these rails with open ends and assumed that they were external connections, and tried to extend them, except they would extend directly into a support pillar.

once these extra pieces were removed the tester ran fine, although the roundabout part of the design rapidly deadlocked as there are no chain signals

the rail bridges issue should be fixed with 0.9.1 (released as i post this)