A new software system for the state’s health insurance website passed its first key test this week, and a final decision on whether Massachusetts will run its own site or join the federal exchange will be made in early August, a top state official said. Maydad Cohen, special adviser to the governor, told the Massachusetts Health Connector board Thursday morning that the new software from hCentive performed every task required by federal officials, and then some, in a Washington, D.C., demonstration Monday. This success, he said in an interview afterward, leaves him increasingly but cautiously optimistic that the state will be able to employ the hCentive software when open enrollment starts Nov. 15.