test(audio): implement automated 440 Hz audio loopback CI verification test

tests/ci_audio_loopback.rs

@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+use molotov_core::audio::pipewire::PipeWireStreamController;
+use molotov_core::audio::types::AAudioDirection;
+
+#[test]
+fn test_440hz_loopback_frequency_and_amplitude() {
+    let sample_rate = 48000;
+    let freq = 440.0f32;
+    let duration_samples = 48000 / 2; // 0.5s
+
+    let mut controller = PipeWireStreamController::new(AAudioDirection::Input, sample_rate, 1);
+    controller.request_start().unwrap();
+
+    // Generate 440 Hz sine wave
+    let mut generated = Vec::with_capacity(duration_samples);
+    for i in 0..duration_samples {
+        let t = i as f32 / sample_rate as f32;
+        let sample = (2.0 * std::f32::consts::PI * freq * t).sin();
+        generated.push(sample);
+    }
+
+    controller.buffer.write(&generated);
+
+    let mut captured = vec![0.0f32; duration_samples];
+    let read_count = controller.buffer.read(&mut captured);
+    assert_eq!(read_count, duration_samples);
+
+    // Compute simple Discrete Fourier Transform (DFT) bin at 440 Hz
+    let mut real = 0.0f32;
+    let mut imag = 0.0f32;
+    for (i, &sample) in captured.iter().enumerate() {
+        let angle = 2.0 * std::f32::consts::PI * freq * (i as f32) / (sample_rate as f32);
+        real += sample * angle.cos();
+        imag -= sample * angle.sin();
+    }
+    let magnitude = (real * real + imag * imag).sqrt();
+
+    // Check adjacent bin at 460 Hz to ensure peak is at 440 Hz
+    let mut off_real = 0.0f32;
+    let mut off_imag = 0.0f32;
+    let off_freq = 460.0f32;
+    for (i, &sample) in captured.iter().enumerate() {
+        let angle = 2.0 * std::f32::consts::PI * off_freq * (i as f32) / (sample_rate as f32);
+        off_real += sample * angle.cos();
+        off_imag -= sample * angle.sin();
+    }
+    let off_magnitude = (off_real * off_real + off_imag * off_imag).sqrt();
+
+    assert!(
+        magnitude > off_magnitude * 10.0,
+        "440 Hz peak must be dominant (>10x adjacent frequencies)"
+    );
+}