From 55ed3610ffb8589505346141604c8b9ea2850e43 Mon Sep 17 00:00:00 2001
From: skal <pascal.massimino@gmail.com>
Date: Wed, 4 Feb 2026 10:57:28 +0100
Subject: test(coverage): Improve Audio coverage (Task #48)

Added unit tests for DCT and procedural audio generation. Enhanced synth tests to cover rendering and resource management. Audio subsystem coverage increased to 93%.
---
 src/tests/test_synth.cc | 78 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 77 insertions(+), 1 deletion(-)

(limited to 'src/tests/test_synth.cc')

diff --git a/src/tests/test_synth.cc b/src/tests/test_synth.cc
index 2594660..c172da1 100644
--- a/src/tests/test_synth.cc
+++ b/src/tests/test_synth.cc
@@ -5,6 +5,7 @@
 #include "audio/synth.h"
 #include <assert.h>
 #include <stdio.h>
+#include <cmath>
 
 void test_registration() {
   synth_init();
@@ -14,6 +15,11 @@ void test_registration() {
   int id = synth_register_spectrogram(&spec);
   assert(id >= 0);
   assert(synth_get_active_voice_count() == 0);
+  
+  synth_unregister_spectrogram(id);
+  // Re-register to check slot reuse
+  int id2 = synth_register_spectrogram(&spec);
+  assert(id2 == id); // Should reuse the slot 0
 }
 
 void test_trigger() {
@@ -26,10 +32,80 @@ void test_trigger() {
   assert(synth_get_active_voice_count() == 1);
 }
 
+void test_render() {
+  synth_init();
+  float data[DCT_SIZE * 2] = {0};
+  // Put some signal in (DC component)
+  data[0] = 100.0f; 
+
+  Spectrogram spec = {data, data, 2};
+  int id = synth_register_spectrogram(&spec);
+  
+  synth_trigger_voice(id, 1.0f, 0.0f);
+  
+  float output[1024] = {0}; 
+  synth_render(output, 256);
+  
+  // Verify output is not all zero (IDCT of DC component should be constant)
+  bool non_zero = false;
+  for(int i=0; i<256; ++i) {
+      if(std::abs(output[i]) > 1e-6f) non_zero = true;
+  }
+  assert(non_zero);
+  
+  // Test render with no voices
+  synth_init(); // Reset
+  float output2[1024] = {0};
+  synth_render(output2, 256);
+  for(int i=0; i<256; ++i) assert(output2[i] == 0.0f);
+}
+
+void test_update() {
+    synth_init();
+    float data[DCT_SIZE * 2] = {0};
+    Spectrogram spec = {data, data, 2};
+    int id = synth_register_spectrogram(&spec);
+    
+    float* back_buf = synth_begin_update(id);
+    assert(back_buf != nullptr);
+    // Write something
+    back_buf[0] = 50.0f;
+    synth_commit_update(id);
+    
+    // Test invalid ID
+    assert(synth_begin_update(-1) == nullptr);
+    synth_commit_update(-1); // Should not crash
+}
+
+void test_exhaustion() {
+    synth_init();
+    float data[DCT_SIZE * 2] = {0};
+    Spectrogram spec = {data, data, 2};
+    
+    for(int i=0; i<MAX_SPECTROGRAMS; ++i) {
+        int id = synth_register_spectrogram(&spec);
+        assert(id >= 0);
+    }
+    // Next one should fail
+    int id = synth_register_spectrogram(&spec);
+    assert(id == -1);
+}
+
+void test_peak() {
+    // Already called render in test_render.
+    // Just call the getter.
+    float peak = synth_get_output_peak();
+    assert(peak >= 0.0f);
+}
+
 int main() {
   printf("Running SynthEngine tests...\n");
   test_registration();
   test_trigger();
+  test_render();
+  test_update();
+  test_exhaustion();
+  test_peak();
   printf("SynthEngine tests PASSED\n");
   return 0;
-}
+}
\ No newline at end of file
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