The Roman army was one that adapted and incorporated other fighting styles or equipment. Development of new technology was never instant and would be something that was phased in upon exposure to new technology or tactics.

The Roman army for example started off fighting as a phalanx which they presumably learnt from the Greek colonies or Etruscans. They next transitioned to the manipular arrangement of the polybian legions possibly in response to fighting in rougher terrain during the Samnite wars. Levies formed into maniples transitioned into professional soldiers formed into cohorts around the 1st century BC gradually due to army recruitment issues and political factors.

Weapons such as the Gladius was adapted from the Iberians, the scutum shield pissibly from the samnites, the ring mail cuirass from the Celts, and the list goes on.

The strength of Rome came from its ability to adapt to the opponents it faced. There was no centralized force developing and testing equipment, this was all virtually done in a reactionary way gradually over time. We aren't sure how the first set of new shields or swords would have come into use. However it seems plausible that Romans bore witness to their effectiveness and acquired them through trade or imitation. Early Roman armies had to provide their own equipment so a soldier might go to a manufacturer/merchant selling new equipment "x" which was said to have superior qualities "y". Over time supply and demand might make this particular equipment more standardized.

I might also point out that the Romans did actually develop the rather novel device known as the Corvus. This was a metal hook attached to the bottom of pivoting boarding bridges that allowed Roman ships to grab enemy vessels and over run them with marines. However this development was only possible after Rome copied the Carthaginian ship designs to be able to have a navy in the first place.

Perhaps the only routine "testing" that got done may have been carried out by skilled generals such as Scipio Africanus or Caesar who developed effective and novel tactics. These would have been passed down the years to other commanders who would often employ strategems from the past.

Hope this helps