The testing and commissioning of any light rail scheme is only one stage of a very comprehensive process. To be honest, if you are interested in the detail behind why a project of the scale of Metrolink requires long timeframes then you might find the website of the Light Rail Transit Association to be of interest: www.lrta.org. Some of the content is very technical, other sections use a little less industry jargon but it is a very good way of explaining the very detailed processes and procedures involved.
The Passenger Transport Executive Group website (www.pteg.net) also has some very interesting articles and also The Trams.co.uk (www.thetrams.co.uk) which provides some good links to official government advice and publications. Some of the government documents are as dull as dishwater to read through but they do give a really thorough insight into what happens "behind the scenes" and they certainly helped me to really appreciate the challenges that are presented to any local authority looking at embarking on anything as ambitious as Metrolink.