HUMZA Yousaf is facing the most testing time of his ministerial career so far.

He is not alone in this as the job of Transport Minister throws up specific events that can make or break a politician.

The SNP has had four Transport Ministers since it took office in 2007 so the post has a shelf life of around two and a half years.

Mr Yousaf has said he will prepare for a public sector bid to compete for the next ScotRail franchise and to be ready should Abellio lose it when there is a break in the contract in 2020.

The chances of Mr Yousaf being in his current post at that time are slim.

Previous experience indicates it will go one of two ways.

Stewart Stevenson, the SNP’s first Transport Minister, made a complete and utter pig’s ear of handling the episode that saw blizzards close much of the motorway network in 2010.

He said the response was “first class” when people were trapped in their cars and on buses for hours on end in the freezing cold winter.

So he had to go.

Keith Brown took over and quickly got the situation under control that year and the following year and won himself a promotion to a cabinet post at Infrastructure.

Then Derek Mackay took over and faced his big test when the Forth Road Bridge had to be shut for essential repairs causing chaos on the roads and railways into Edinburgh.

That could have ended his career and there were many calls for his resignation but he dealt with the challenge and the criticism and came through it with his reputation enhanced.

He then landed one of the top government jobs as Finance Secretary.

Ministerial politics is like a game of snakes and ladders. While Mr Stevenson slid down the snake, His two successors have climbed the ladder.

Now Humza Yousaf has rolled the dice with his improvement plan, threat of removing the contract from Abellio if it doesn’t improve and plans for the public sector to be able to bid.

Labour and the Tories have had the scent of ministerial blood in their nostrils since that train broke down outside Waverley Station last week crippling the rail network.

Since then every delay and disruption has come under scrutiny with calls for Mr Yousaf to get a grip.

He has apologised in parliament to passengers who have had a poor service and has outlined the improvement plan and what he expects Abellio to deliver in terms of reliability and punctuality.

Passengers want affordable, comfortable trains they can get a seat on which arrive on time.

For the most part they do, but those days which begin with a half hour wait on a cold wet platform listening to a recorded announcement telling you “ScotRail is sorry to announce…. “gets the travelling public’s backs up.

If Mr Yousaf gets this sorted his reputation will grow and his career will carry on the upward trajectory it has so far enjoyed.

But if he is unable get Abellio to improve the only outcome will be “the next minister to depart from Holyrood station will be Humza Yousaf.