exec: increase default wait delay

Should avoid killing Nix command whenever possible.

exec.go

@@ -11,7 +11,7 @@ import (
 )
 
 const (
-	defaultWaitDelay = 15 * time.Second
+	defaultWaitDelay = 30 * time.Second
 )
 
 // Nix is the name of the nix program.

exec_stub_test.go

@@ -107,7 +107,7 @@ func TestNixStub(t *testing.T) {
 		Flag(&flagExtraExperimentalFeatures, trimFlagName(nix.ExtraExperimentalFeatures), command.StringFlag(""),
 			fmt.Sprintf("expects exactly %q", nix.ExperimentalFeaturesFlakes))
 
-	c.Command("true", command.UsageInternal, func([]string) error { return nil })
+	c.Command(nix.ValueTrue, command.UsageInternal, func([]string) error { return nil })
 
 	for _, f := range stubCommandInit {
 		f(c)

exec_test.go

@@ -1,6 +1,7 @@
 package nix_test
 
 import (
+	"context"
 	"errors"
 	"os"
 	"os/exec"
@@ -33,4 +34,23 @@ func TestNixWriteStdin(t *testing.T) {
 			t.Fatalf("WriteStdinCommand: error = %v, want %v", err, syscall.ENOSYS)
 		}
 	})
+
+	t.Run("exit before cancel", func(t *testing.T) {
+		stubNixCommand(t)
+		ctx := newStubContext(t.Context(), nil, os.Stdout, os.Stderr)
+		c, cancel := context.WithCancel(t.Context())
+		defer cancel()
+		cmd := ctx.Nix(c, "true")
+		if err := cmd.Start(); err != nil {
+			t.Fatalf("Start: error = %v", err)
+		}
+		// Cancel is skipped after exec.Cmd.Wait completes
+		if _, err := cmd.Process.Wait(); err != nil {
+			t.Fatalf("Wait: error = %v", err)
+		}
+		cancel()
+		if cmd.Err != nil {
+			t.Fatalf("Err = %v", cmd.Err)
+		}
+	})
 }