diff --git a/applypatch/imgdiff_test.sh b/applypatch/imgdiff_test.sh
new file mode 100755
index 0000000..dcdb922
--- /dev/null
+++ b/applypatch/imgdiff_test.sh
@@ -0,0 +1,118 @@
+#!/bin/bash
+#
+# A script for testing imgdiff/applypatch.  It takes two full OTA
+# packages as arguments.  It generates (on the host) patches for all
+# the zip/jar/apk files they have in common, as well as boot and
+# recovery images.  It then applies the patches on the device (or
+# emulator) and checks that the resulting file is correct.
+
+EMULATOR_PORT=5580
+
+# set to 0 to use a device instead
+USE_EMULATOR=0
+
+# where on the device to do all the patching.
+WORK_DIR=/data/local/tmp
+
+START_OTA_PACKAGE=$1
+END_OTA_PACKAGE=$2
+
+# ------------------------
+
+tmpdir=$(mktemp -d)
+
+if [ "$USE_EMULATOR" == 1 ]; then
+  emulator -wipe-data -noaudio -no-window -port $EMULATOR_PORT &
+  pid_emulator=$!
+  ADB="adb -s emulator-$EMULATOR_PORT "
+else
+  ADB="adb -d "
+fi
+
+echo "waiting to connect to device"
+$ADB wait-for-device
+
+# run a command on the device; exit with the exit status of the device
+# command.
+run_command() {
+  $ADB shell "$@" \; echo \$? | awk '{if (b) {print a}; a=$0; b=1} END {exit a}'
+}
+
+testname() {
+  echo
+  echo "$1"...
+  testname="$1"
+}
+
+fail() {
+  echo
+  echo FAIL: $testname
+  echo
+  [ "$open_pid" == "" ] || kill $open_pid
+  [ "$pid_emulator" == "" ] || kill $pid_emulator
+  exit 1
+}
+
+sha1() {
+  sha1sum $1 | awk '{print $1}'
+}
+
+size() {
+  stat -c %s $1 | tr -d '\n'
+}
+
+cleanup() {
+  # not necessary if we're about to kill the emulator, but nice for
+  # running on real devices or already-running emulators.
+  testname "removing test files"
+  run_command rm $WORK_DIR/applypatch
+  run_command rm $WORK_DIR/source
+  run_command rm $WORK_DIR/target
+  run_command rm $WORK_DIR/patch
+
+  [ "$pid_emulator" == "" ] || kill $pid_emulator
+
+  rm -rf $tmpdir
+}
+
+$ADB push $ANDROID_PRODUCT_OUT/system/bin/applypatch $WORK_DIR/applypatch
+
+patch_and_apply() {
+  local fn=$1
+  shift
+
+  unzip -p $START_OTA_PACKAGE $fn > $tmpdir/source
+  unzip -p $END_OTA_PACKAGE $fn > $tmpdir/target
+  imgdiff "$@" $tmpdir/source $tmpdir/target $tmpdir/patch
+  bsdiff $tmpdir/source $tmpdir/target $tmpdir/patch.bs
+  echo "patch for $fn is $(size $tmpdir/patch) [of $(size $tmpdir/target)] ($(size $tmpdir/patch.bs) with bsdiff)"
+  echo "$fn $(size $tmpdir/patch) of $(size $tmpdir/target) bsdiff $(size $tmpdir/patch.bs)" >> /tmp/stats.txt
+  $ADB push $tmpdir/source $WORK_DIR/source || fail "source push failed"
+  run_command rm /data/local/tmp/target
+  $ADB push $tmpdir/patch $WORK_DIR/patch || fail "patch push failed"
+  run_command /data/local/tmp/applypatch /data/local/tmp/source \
+    /data/local/tmp/target $(sha1 $tmpdir/target) $(size $tmpdir/target) \
+    $(sha1 $tmpdir/source):/data/local/tmp/patch \
+    || fail "applypatch of $fn failed"
+  $ADB pull /data/local/tmp/target $tmpdir/result
+  diff -q $tmpdir/target $tmpdir/result || fail "patch output not correct!"
+}
+
+# --------------- basic execution ----------------------
+
+for i in $((zipinfo -1 $START_OTA_PACKAGE; zipinfo -1 $END_OTA_PACKAGE) | \
+           sort | uniq -d | egrep -e '[.](apk|jar|zip)$'); do
+  patch_and_apply $i -z
+done
+patch_and_apply boot.img
+patch_and_apply system/recovery.img
+
+
+# --------------- cleanup ----------------------
+
+cleanup
+
+echo
+echo PASS
+echo
+