Open tone-test output before transmission

tonetest_test.go

@@ -0,0 +1,15 @@
+package main
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+// Regression: tone transmission was started before opening its output file,
+// so a creation error left audio transmission running without cleanup.
+func TestNewAudioFileSaverReportsUnavailableOutputPath(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "missing", "tone.pcm")
+	if saver, err := NewAudioFileSaver(path); err == nil || saver != nil {
+		t.Fatalf("got saver=%v err=%v", saver, err)
+	}
+}