test(shell): cover emulated shell branches

pkg/shell/shell_test.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"fmt"
 	"os"
+	"strings"
 	"testing"
 )
 
@@ -27,3 +28,63 @@ func TestRunEmulatedShell_KillExecutesRealBinary(t *testing.T) {
 		)
 	}
 }
+
+func TestRunEmulatedShell_ParseError(t *testing.T) {
+	err := RunEmulatedShell(
+		context.Background(),
+		&CommandRunner{
+			Command: "if then fi (((( broken syntax",
+			Stdout:  &bytes.Buffer{},
+			Stderr:  &bytes.Buffer{},
+			Environ: os.Environ(),
+		},
+	)
+	if err == nil {
+		t.Fatal("expected parse error for malformed command, got nil")
+	}
+	if !strings.Contains(err.Error(), "parse shell command") {
+		t.Fatalf("expected 'parse shell command' error, got: %v", err)
+	}
+}
+
+func TestRunEmulatedShell_DevNullRedirect(t *testing.T) {
+	var stdout, stderr bytes.Buffer
+	err := RunEmulatedShell(
+		context.Background(),
+		&CommandRunner{
+			Command: "echo suppressed > /dev/null; echo visible",
+			Stdout:  &stdout,
+			Stderr:  &stderr,
+			Environ: os.Environ(),
+		},
+	)
+	if err != nil {
+		t.Fatalf("expected nil error, got: %v\nstderr: %s", err, stderr.String())
+	}
+	if stdout.String() != "visible\n" {
+		t.Fatalf("expected only 'visible' on stdout, got: %q", stdout.String())
+	}
+}
+
+func TestRunEmulatedShell_NilEnvFallsBackToSystem(t *testing.T) {
+	var stdout, stderr bytes.Buffer
+	err := RunEmulatedShell(
+		context.Background(),
+		&CommandRunner{
+			Command: "echo $HOME",
+			Stdout:  &stdout,
+			Stderr:  &stderr,
+			Environ: nil,
+		},
+	)
+	if err != nil {
+		t.Fatalf("expected nil error, got: %v\nstderr: %s", err, stderr.String())
+	}
+	home := os.Getenv("HOME")
+	if home == "" {
+		t.Skip("HOME not set, cannot verify env fallback")
+	}
+	if !strings.Contains(stdout.String(), home) {
+		t.Fatalf("expected stdout to contain HOME=%q, got: %q", home, stdout.String())
+	}
+}