fm-rds-tx/internal/stereo/encoder_test.go

package stereo

import (
	"math"
	"testing"

	"github.com/jan/fm-rds-tx/internal/audio"
)

func TestStereoEncoderEncode(t *testing.T) {
	enc := NewStereoEncoder(228000)
	frame := audio.NewFrame(1, -1)
	result := enc.Encode(frame)

	if diff := result.Mono; math.Abs(diff) > 1e-9 {
		t.Fatalf("expected mono 0, got %v", diff)
	}

	// Stereo should be non-zero for L!=R input
	// (exact value depends on oscillator phase at sample 0)
	// We just verify it's modulated (could be zero at phase=0 for sin)
	// Run a few samples and check some are non-zero
	var maxStereo float64
	for i := 0; i < 100; i++ {
		c := enc.Encode(frame)
		if math.Abs(c.Stereo) > maxStereo {
			maxStereo = math.Abs(c.Stereo)
		}
	}
	if maxStereo < 0.1 {
		t.Fatalf("expected non-trivial stereo signal, maxStereo=%.6f", maxStereo)
	}
}

func TestStereoEncoderMonoSignal(t *testing.T) {
	enc := NewStereoEncoder(228000)
	// Identical L and R should produce zero difference/stereo
	frame := audio.NewFrame(0.5, 0.5)
	for i := 0; i < 100; i++ {
		c := enc.Encode(frame)
		if math.Abs(c.Stereo) > 1e-12 {
			t.Fatalf("expected zero stereo for mono input, got %.9f", c.Stereo)
		}
		if math.Abs(c.Mono-0.5) > 1e-9 {
			t.Fatalf("expected mono=0.5, got %.9f", c.Mono)
		}
	}
}

func TestStereoEncoderPilotRange(t *testing.T) {
	enc := NewStereoEncoder(228000)
	frame := audio.NewFrame(0.1, -0.1)
	for i := 0; i < 1000; i++ {
		c := enc.Encode(frame)
		if c.Pilot < -0.101 || c.Pilot > 0.101 {
			t.Fatalf("pilot out of range: %.6f", c.Pilot)
		}
	}
}

func TestStereoEncoderReset(t *testing.T) {
	frame := audio.NewFrame(0.1, -0.1)
	enc := NewStereoEncoder(228000)

	initial := make([]float64, 0, 4)
	for i := 0; i < 4; i++ {
		initial = append(initial, enc.Encode(frame).Pilot)
	}

	enc.Reset()

	afterReset := make([]float64, 0, 4)
	for i := 0; i < 4; i++ {
		afterReset = append(afterReset, enc.Encode(frame).Pilot)
	}

	for i := range initial {
		if math.Abs(initial[i]-afterReset[i]) > 1e-9 {
			t.Fatalf("reset failed at sample %d: %v vs %v", i, initial[i], afterReset[i])
		}
	}
}