The first tram set off along Broad Street, stopping at the end of the new line at Edgbaston Village.
Further trials will now be carried out ahead of passenger services in June.
Meanwhile, trams across the remaining network are still suspended for safety reasons, but transport bosses say services should resume in May.
Bodywork cracks found on older trams led to the fleet being suspended in November before returning in February only to be stopped again last month.
Peter Cushing, Director of the Midland Metro Alliance (MMA), said the latest journey was a "significant milestone" for the Birmingham Westside Metro extension.
"It is fantastic that the first tram has now travelled along Broad Street as testing of the new route begins," he said.
"This marks a significant milestone in the project and shows just how close we are to opening for passenger services."
The testing programme will also allow people to get used to trams travelling at low speeds along Broad Street and Hagley Road, the MMA said.
When the route opens in June, passengers can get on and off at three new stops along the Broad Street and Hagley Road route.
Meanwhile, West Midlands Metro, who operate the tram network, has confirmed the tram fleet has been assessed and work to replace cracked body panels was under way to enable the vehicles to return to service as quickly as possible.