Add a script for doing very rudimentary regression testing

This is expected to fail if the encoder is updated in a way
that changes its output; in such cases, the test references need
to be updated.

test/ref-mono.txt

@@ -0,0 +1,2 @@
+encode hash: 516e51016cbba6068f1aa285a8fdd55b00ada6b0
+decode hash: 3b3b3a17cc5ba50ade75b3ef1a37f96017935fe5

test/ref-stereo.txt

@@ -0,0 +1,2 @@
+encode hash: 1179940ca3a5c62de45b6823efbdbe42fce11de2
+decode hash: 85f2a154b46cc6cfa2792ff95c67b4200ce4463b

test/run-test.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+
+set -e
+set -o pipefail
+
+if [ ! -f Sample01_4.wav ]; then
+	curl -LO https://media.xiph.org/audio/HA_2011/Sample01_4.wav
+fi
+
+if [ "$(md5sum Sample01_4.wav | awk '{print $1}')" != "a5c105544c64ce92c6c5c06d280e6b9c" ]; then
+	echo Incorrect checksum for Sample01_4.wav
+	exit 1
+fi
+
+if [ ! -f Sample01_4-mono.wav ]; then
+	ffmpeg -i Sample01_4.wav -ac 1 -fflags +bitexact -y Sample01_4-mono.wav
+fi
+
+if [ "$(md5sum Sample01_4-mono.wav | awk '{print $1}')" != "3bfccac9f2e527ba3ef888874f09a409" ]; then
+	echo Incorrect checksum for Sample01_4-mono.wav
+	exit 1
+fi
+
+./test-encode-decode Sample01_4.wav | tee log-stereo.txt
+./test-encode-decode Sample01_4-mono.wav | tee log-mono.txt
+
+diff -u log-stereo.txt $(dirname $0)/ref-stereo.txt
+diff -u log-mono.txt $(dirname $0)/ref-mono.txt