BlackRock recently tested its new bond-trading platform without telling the Wall Street securities dealers that dominate that business, a move that miffed some traders at the banks in the latest sign of tension over who ultimately will control securities trading.

The New York money manager's BlackRock Solutions arm last Thursday held a live trading session with several members of its Aladdin Trading Network, the name of its new electronic trading hub. The platform is designed to let BlackRock and other large investors-from sovereign wealth funds to mutual-fund companies-trade corporate bonds directly with each other, bypassing Wall Street and lowering trading costs.