In reply to kevinvig7:
Will you still instantiate the agent’s interface in your testbench? If so, you can use a ‘mode’ variable in the interface which you can use to determine whether to drive the interface outputs from internal variables or idle states.
interface my_if;
// Wires to connect to design
wire my_if_a_wire;
// Internal variables to be driven by agent
reg my_if_a_reg;
bit mode = 0; // 0 if idle, 1 if active
assign my_if_a_wire = (mode == 0) ? 1'b0 : my_if_a_reg;
endinterface
If you don’t instantiate the interface, you will need to assign the signals directly in your testbench.