helper: test non-existent helpers

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

helper/helper.go

@@ -96,13 +96,15 @@ func (h *Helper) StartNotify(ready chan error) error {
 	// write arguments and close args pipe
 	if _, err := h.args.WriteTo(argsP); err != nil {
 		if err1 := h.Cmd.Process.Kill(); err1 != nil {
-			panic(err1)
+			// should be unreachable
+			panic(err1.Error())
 		}
 		return err
 	} else {
 		if err = argsP.Close(); err != nil {
 			if err1 := h.Cmd.Process.Kill(); err1 != nil {
-				panic(err1)
+				// should be unreachable
+				panic(err1.Error())
 			}
 			return err
 		}
@@ -117,7 +119,8 @@ func (h *Helper) StartNotify(ready chan error) error {
 			switch n {
 			case -1:
 				if err1 := h.Cmd.Process.Kill(); err1 != nil {
-					panic(err1)
+					// should be unreachable
+					panic(err1.Error())
 				}
 				// ensure error is not nil
 				if err == nil {
@@ -155,18 +158,22 @@ func (h *Helper) Wait() error {
 	// ensure pipe close
 	defer func() {
 		if err := h.argsP[0].Close(); err != nil && !errors.Is(err, os.ErrClosed) {
-			panic(err)
+			// unreachable
+			panic(err.Error())
 		}
 		if err := h.argsP[1].Close(); err != nil && !errors.Is(err, os.ErrClosed) {
-			panic(err)
+			// unreachable
+			panic(err.Error())
 		}
 
 		if h.ready != nil {
 			if err := h.statP[0].Close(); err != nil && !errors.Is(err, os.ErrClosed) {
-				panic(err)
+				// unreachable
+				panic(err.Error())
 			}
 			if err := h.statP[1].Close(); err != nil && !errors.Is(err, os.ErrClosed) {
-				panic(err)
+				// unreachable
+				panic(err.Error())
 			}
 		}
 	}()

helper/helper_test.go

@@ -1,7 +1,9 @@
 package helper_test
 
 import (
+	"errors"
 	"io"
+	"os"
 	"strings"
 	"sync"
 	"testing"
@@ -38,6 +40,15 @@ func TestHelper_StartNotify_Close_Wait(t *testing.T) {
 	helper.InternalReplaceExecCommand(t)
 	argsOnce.Do(prepareArgs)
 
+	t.Run("start non-existent helper path", func(t *testing.T) {
+		h := helper.New(argsWt, "/nonexistent")
+
+		if err := h.Start(); !errors.Is(err, os.ErrNotExist) {
+			t.Errorf("Start() error = %v, wantErr %v",
+				err, os.ErrNotExist)
+		}
+	})
+
 	t.Run("start helper with status channel", func(t *testing.T) {
 		h := helper.New(argsWt, "crash-test-dummy", "--args=3", "--fd=4")
 		ready := make(chan error, 1)

helper/stub.go

@@ -85,6 +85,11 @@ func InternalReplaceExecCommand(t *testing.T) {
 
 	// replace execCommand to have the resulting *exec.Cmd launch TestHelperChildStub
 	execCommand = func(name string, arg ...string) *exec.Cmd {
+		// pass through nonexistent path
+		if name == "/nonexistent" && len(arg) == 0 {
+			return exec.Command(name)
+		}
+
 		return exec.Command(os.Args[0], append([]string{"-test.run=TestHelperChildStub", "--", name}, arg...)...)
 	}
 }