BERLIN – Six European Union countries and the bloc's executive Commission have begun testing a virtual “gateway” to ensure national coronavirus tracing apps can work across borders.The trial starting Monday will allow national computer systems that run tracing apps in the Czech Republic, Denmark, Germany, Ireland, Italy and Latvia to communicate with each other via a central hub.If the tests succeed, travelers from each of the six countries will be able to use their own apps while abroad in the other five to ensure they're notified if they have been in close contact to another user who tests positive.Tracing apps were touted as a potentially game-changing tool to reduce the spread of COVID-19, but most have been beset with privacy concerns,.