add furnace test suite

.gitignore

@@ -9,3 +9,6 @@ linuxbuild/
 *.swp
 .cache/
 .DS_Store
+test/songs/
+test/delta/
+test/result/

test/furnace-test.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+# renders all files in test/songs/ and outputs them for delta testing.
+# useful when doing changes to playback.
+# requires GNU parallel.
+
+testDir=$(date +%Y%m%d%H%M%S)
+if [ -e "test/result" ]; then
+  lastTest=$(ls "test/result" | tail -2 | head -1 || echo "")
+else
+  lastTest=""
+fi
+
+echo "lastTest is $lastTest"
+
+echo "furnace test suite begin..."
+echo "--- STEP 1: render test files"
+mkdir -p "test/result/$testDir" || exit 1
+ls "test/songs/" | parallel --verbose -j4 ./build/furnace -output "test/result/$testDir/{0}.wav" "test/songs/{0}"
+echo "--- STEP 2: calculate deltas"
+if [ -z $lastTest ]; then
+  echo "skipping since this apparently is your first run."
+else
+  mkdir -p "test/delta/$testDir" || exit 1
+  ls "test/result/$testDir/" | parallel --verbose -j4 ffmpeg -i "test/result/$lastTest/{0}" -i "test/result/$testDir/{0}" -filter_complex stereotools=phasel=1:phaser=1,amix=inputs=2:duration=longest -c:a pcm_s16le -y "test/delta/$testDir/{0}"
+fi
+echo "--- STEP 3: make delta images"
+if [ -z $lastTest ]; then
+  echo "skipping since this apparently is your first run."
+else
+  ls "test/result/$testDir/" | parallel --verbose -j4 ffmpeg -i "test/delta/$testDir/{0}" -lavfi showspectrumpic "test/delta/$testDir/{0}.png"
+fi