test: playing a recording must not consume it

Reported: the recording plays once and never again, "as if it threw the sound
away after playing it". PeekQSO is what the playback reads and it is meant to
copy — TakeQSO is the one that clears — so this pins that, and that the copy is
independent of the recorder's own buffer.

It passes, which is the useful part: the take survives, so the one-shot failure
is downstream of it and the search moves to the file and the player.

internal/audio/peek_test.go

@@ -0,0 +1,56 @@
+package audio
+
+import (
+	"testing"
+	"time"
+)
+
+// Playing a stopped take must not consume it.
+//
+// Reported on the air: the recording plays once, then nothing — "as if it threw
+// the sound away after playing it". PeekQSO is what the playback reads, and it
+// is meant to COPY; TakeQSO is the one that clears.
+func TestPeekDoesNotConsumeTheTake(t *testing.T) {
+	r := &Recorder{running: true, active: true, paused: true, prerollSamples: sampleRate}
+	r.acc = make([]int16, 4000)
+	for i := range r.acc {
+		r.acc[i] = int16(i % 500)
+	}
+
+	first, err := r.PeekQSO()
+	if err != nil {
+		t.Fatalf("first peek: %v", err)
+	}
+	second, err := r.PeekQSO()
+	if err != nil {
+		t.Fatalf("second peek: %v — the take was consumed by the first", err)
+	}
+	if len(first) != len(second) {
+		t.Errorf("second peek returned %d bytes, first %d", len(second), len(first))
+	}
+
+	// And the copy must be independent: the caller holds these bytes while the
+	// recorder may still be appending to its own slice.
+	if len(first) > 0 {
+		first[0] = ^first[0]
+		again, _ := r.PeekQSO()
+		if len(again) > 0 && again[0] == first[0] {
+			t.Error("PeekQSO handed out its internal buffer, not a copy")
+		}
+	}
+
+	// Resuming and stopping again keeps everything captured so far.
+	r.ResumeQSO()
+	r.mu.Lock()
+	r.acc = append(r.acc, make([]int16, 1000)...)
+	r.mu.Unlock()
+	r.PauseQSO()
+	third, err := r.PeekQSO()
+	if err != nil {
+		t.Fatalf("peek after resume: %v", err)
+	}
+	if len(third) <= len(second) {
+		t.Errorf("after resuming, the take is %d bytes — it should have grown past %d", len(third), len(second))
+	}
+	_ = time.Now
+}