His first big electoral test comes next week.The Conservatives, propped up in power by Northern Ireland’s Democratic Unionist Party, have a working majority of just two.Even that very slim advantage is set to be eroded further on Thursday, August 1, with a crunch by-election in mid-Wales.The rural constituency of Brecon and Radnorshire is up for grabs after the sitting Tory MP Chris Davies was ousted by a recall petition following his criminal conviction for fiddling his parliamentary expenses.Inexplicably - given the embarrassment, chaos and jeopardy he brought on his party - he has been chosen again to fight the seat.The Conservatives have a 8,038 majority.But Remainer parties have rallied behind the candidate with the best chance of winning - Lib Dem Jane Dodds - so they do not split the vote.Consequently, the Lib Dems are tipped to triumph and reclaim the constituency they held until 2015 - inflicting an early wound on the new PM.