How to Send SIGTERM signal to test agent

Hi,

I want to write test case to verify that agent is gracefully shutting down on SIGTERM signal.
However i am not sure how to send a SIGTERM to the running test agent.
Here is what i have come up so far.

	a1 := agent.NewTestAgent(t, ``)
	defer a1.Shutdown()

The above code will start a test agent. I want to send a SIGTERM to this and verify its gracefully shutting down.

Ref: consul/testagent.go at 214495f2a27bf05dc4b610384894cdfcea3fa115 · hashicorp/consul · GitHub