Ireland provide the warm-up for the looming Ashes series but England captain Joe Root refuses to view the outcome of the four-day Test as a formality.

"Ireland are a side that have always performed well, probably over performed at times," Root said.

"I hope that doesn't sound that I am underestimating them or not giving them a fair shout - they have upset sides like England in previous World Cups and they ran us close in the one day format at the start of the year.

"Their Test match last summer against Pakistan was a brilliant game. I thought they played really well and proved that they deserved Test status.

"It is great for the game that sides like Ireland are getting a chance in this format and I think they have earned the right to get this fixture." 

Jason Roy will make his Test debut against Ireland at Lord's reassured by instructions from England captain Root to play his natural game.

Roy will open the batting in the hope the attacking instincts that have served England so well in limited overs cricket, including the recent World Cup triumph, will translate to the longer form.

Root believes the Surrey batsman has the skills to defend if needed, but insists the team will be best served if he takes the game to Ireland.

"We want Jason to go out and be himself, to express himself and trust his instincts as much as possible," Root said.

"He's got very good instincts, he reads the game very well and he brings something different to our Test batting line-up.

"He's a very exciting prospect and a proven performer at international cricket. He's capable of making big contributions at the top of the order.

"I hope he doesn't try to play differently. Only in small pockets, but we've seen throughout the World Cup that he can soak up pressure and trust his defence. It might be that he has to do that for longer in Test cricket.

"But there are times when he can put pressure back on to the opposition and he's one of the best in the world at doing that."