Police canvassed the area, but did not find anyone who posed a threat.
Two remain hospitalized with non-life-threatening injuries, police say.
The testing, which started in October, will continue into the spring semester.
Trails in the College Park, Hyattsville, Riverdale Park and Bladensburg areas will be closed until further notice.
Preliminarily, police do not believe that this is a random shooting.
UMPD’s Criminal Investigations Unit is investigating this incident, according to the notice.
The two suspects were last seen armed with a handgun and running behind the store.
While some groups have launched committees, others say that change requires action.
Police told residents to steer clear of the area.
The Metro Transit Police Department will be conducting the robbery investigation.