*: add and expose StopSignal field in ExpectProcess

add and expose StopSignal to ExpectProcess allows user
to define what signal to send on ExpectProcess.close()

coverage testing code sets StopSignal to SIGTERM allowing
the test binary to shutdown gracefully so that it can generate
a coverage report.

pkg/expect/expect.go

@@ -23,6 +23,7 @@ import (
 	"os/exec"
 	"strings"
 	"sync"
+	"syscall"
 
 	"github.com/kr/pty"
 )
@@ -38,6 +39,9 @@ type ExpectProcess struct {
 	lines []string
 	count int // increment whenever new line gets added
 	err   error
+
+	// StopSignal is the signal Stop sends to the process; defaults to SIGKILL.
+	StopSignal os.Signal
 }
 
 var printDebugLines = os.Getenv("EXPECT_DEBUG") != ""
@@ -52,7 +56,10 @@ func NewExpect(name string, arg ...string) (ep *ExpectProcess, err error) {
 func NewExpectWithEnv(name string, args []string, env []string) (ep *ExpectProcess, err error) {
 	cmd := exec.Command(name, args...)
 	cmd.Env = env
-	ep = &ExpectProcess{cmd: cmd}
+	ep = &ExpectProcess{
+		cmd:        cmd,
+		StopSignal: syscall.SIGKILL,
+	}
 	ep.cond = sync.NewCond(&ep.mu)
 	ep.cmd.Stderr = ep.cmd.Stdout
 	ep.cmd.Stdin = nil
@@ -140,7 +147,7 @@ func (ep *ExpectProcess) close(kill bool) error {
 		return ep.err
 	}
 	if kill {
-		ep.Signal(os.Interrupt)
+		ep.Signal(ep.StopSignal)
 	}
 
 	err := ep.cmd.Wait()