Full operations will get underway on the 5.9km route in December
The first trams are being tested on the Luas Cross City line this weekend.
The 'gauge run' involves two trams being brought 'at walking speeds' between St Stephen's Green and Cabra.
Tests and measurements are being carried out along the 5.9km route, while the trams are also being stopped at each new platform.
The tests got underway this morning, and will include both the northbound and southbound lines. Tests will continue tomorrow.
LCC tram testing now on OConnell Street. pic.twitter.com/GrTMoBsBrZ— Luas Cross City (@LuasCrossCity) June 17, 2017
The National Transport Authority has hailed the test as a 'key milestone' in the project ahead of full operations getting underway in December.
Transport Minister Shane Ross said: “I recognise that the past few years have been challenging for the city and for businesses and we are all looking forward to the works drawing to a close and the start of operations by the end of the year.
"I have no doubt that Luas Cross City will bring huge benefits to the city, including to the businesses in the city centre and along its route and I am very much looking forward to seeing it up and running.”
Dublin Chamber, meanwhile, says today's test shows that an 'end is in sight' for the project, which has led to disruption and major construction work along the new route in recent years.
The organisation's CEO Mary Rose Burke argued: "The new line has been a complicated task and has resulted in significant upheaval over the past four years. But it's very much a case of short-term pain for long-term gain, with the city set to reap the benefits of the new line for decades to come.
"The focus of everyone involved in the project must now be on finishing the job as early as possible before Christmas. An early December opening presents all city centre stakeholders with an opportunity to encourage people to come in and enjoy the city centre this Christmas," she added.