diff --git a/fs_mgr/tests/adb-remount-test.sh b/fs_mgr/tests/adb-remount-test.sh
new file mode 100755
index 0000000..d4ca574
--- /dev/null
+++ b/fs_mgr/tests/adb-remount-test.sh
@@ -0,0 +1,264 @@
+#! /bin/bash
+#
+# adb remount tests (overlayfs focus)
+#
+# Conditions:
+#  - Must be a userdebug build.
+#  - Must be in adb mode.
+#  - Kernel must have overlayfs enabled and patched to support override_creds.
+#  - Must have either squashfs, ext4-dedupe or right-sized partitions.
+#  - Minimum expectation system and vender are overlayfs covered partitions.
+#
+
+# Helper Variables
+
+SPACE=" "
+# A _real_ embedded tab character
+TAB="`echo | tr '\n' '\t'`"
+# A _real_ embedded escape character
+ESCAPE="`echo | tr '\n' '\033'`"
+GREEN="${ESCAPE}[38;5;40m"
+RED="${ESCAPE}[38;5;196m"
+ORANGE="${ESCAPE}[38;5;255:165:0m"
+NORMAL="${ESCAPE}[0m"
+
+# Helper functions
+
+[ "USAGE: inFastboot
+
+Returns: true if device is in fastboot mode" ]
+inFastboot() {
+  fastboot devices | grep "^${ANDROID_SERIAL}[${SPACE}${TAB}]" > /dev/null
+}
+
+[ "USAGE: inAdb
+
+Returns: true if device is in adb mode" ]
+inAdb() {
+  adb devices | grep -v 'List of devices attached' | grep "^${ANDROID_SERIAL}[${SPACE}${TAB}]" > /dev/null
+}
+
+[ "USAGE: adb_sh <commands>
+
+Returns: true if the command succeeded" ]
+adb_sh() {
+  adb shell "${@}"
+}
+
+[ "USAGE: get_property <prop>
+
+Returns the property value" ]
+get_property() {
+  adb_sh getprop ${1} 2>&1 </dev/null
+}
+
+[ "USAGE: isDebuggable
+
+Returns: true if device is (likely) a debug build" ]
+isDebuggable() {
+  if inAdb && [ 1 -ne `get_property ro.debuggable` ]; then
+    false
+  fi
+}
+
+[ "USAGE: adb_su <commands>
+
+Returns: true if the command running as root succeeded" ]
+adb_su() {
+  adb_sh su root "${@}"
+}
+
+[ "USAGE: adb_cat <file> >stdout
+
+Returns: content of file to stdout with carriage returns skipped,
+         true of the file exists" ]
+adb_cat() {
+    OUTPUT="`adb_sh cat ${1} </dev/null 2>&1`"
+    retval=${?}
+    echo "${OUTPUT}" | tr -d '\r'
+    return ${retval}
+}
+
+[ "USAGE: adb_reboot
+
+Returns: true if the reboot command succeeded" ]
+adb_reboot() {
+  adb reboot remount-test
+}
+
+[ "USAGE: adb_wait
+
+Returns: waits until the device has returned" ]
+adb_wait() {
+  adb wait-for-device
+}
+
+[ "USAGE: adb_root
+
+Returns: true if device in root state" ]
+adb_root() {
+  adb root >/dev/null </dev/null 2>&1 &&
+  sleep 1 &&
+  adb_wait &&
+  sleep 1
+}
+
+die() {
+  echo "${RED}[  FAILED  ]${NORMAL} ${@}" >&2
+  exit 1
+}
+
+[ "USAGE: EXPECT_EQ <lval> <rval> [message]
+
+Returns true if (regex) lval matches rval" ]
+EXPECT_EQ() {
+  lval="${1}"
+  rval="${2}"
+  shift 2
+  if ! ( echo X"${rval}" | grep '^X'"${lval}"'$' >/dev/null 2>/dev/null ); then
+    if [ `echo ${lval}${rval}${*} | wc -c` -gt 50 -o "${rval}" != "${rval%
+*}" ]; then
+      echo "ERROR: expected \"${lval}\"" >&2
+      echo "       got \"${rval}\"" |
+        sed ': again
+             N
+             s/\(\n\)\([^ ]\)/\1             \2/
+             t again' >&2
+      if [ -n "${*}" ] ; then
+        echo "       ${*}" >&2
+      fi
+    else
+      echo "ERROR: expected \"${lval}\" got \"${rval}\" ${*}" >&2
+    fi
+    return 1
+  fi
+  if [ -n "${*}" ] ; then
+    if [ X"${lval}" != X"${rval}" ]; then
+      if [ `echo ${lval}${rval}${*} | wc -c` -gt 60 -o "${rval}" != "${rval% *}" ]; then
+        echo "INFO: ok \"${lval}\"" >&2
+        echo "       = \"${rval}\"" |
+          sed ': again
+               N
+               s/\(\n\)\([^ ]\)/\1          \2/
+               t again' >&2
+        if [ -n "${*}" ] ; then
+          echo "      ${*}" >&2
+        fi
+      else
+        echo "INFO: ok \"${lval}\" = \"${rval}\" ${*}" >&2
+      fi
+    else
+      echo "INFO: ok \"${lval}\" ${*}" >&2
+    fi
+  fi
+  return 0
+}
+
+[ "USAGE: check_eq <lval> <rval> [message]
+
+Exits if (regex) lval mismatches rval" ]
+check_eq() {
+  left="${1}"
+  right="${2}"
+  shift 2
+  EXPECT_EQ "${left}" "${right}" ||
+    die "${@}"
+}
+
+[ "USAGE: skip_administrative_mounts
+
+Filters out all administrative (eg: sysfs) mounts" ]
+skip_administrative_mounts() {
+  grep -v -e "^\(overlay\|tmpfs\|none\|sysfs\|proc\|selinuxfs\|debugfs\|bpf\|cg2_bpf\|pstore\|tracefs\|adb\|mtp\|ptp\|devpts\|/data/media\) " -e " /\(cache\|mnt/scratch\|mnt/vendor/persist\|metadata\|data\) "
+}
+
+if [ X"-s" = X"${1}" -a -n "${2}" ]; then
+  export ANDROID_SERIAL="${2}"
+  shift 2
+fi
+
+inFastboot && die "device in fastboot mode"
+inAdb || die "device not in adb mode"
+isDebuggable || die "device not a debug build"
+
+# Do something
+adb_wait || die "wait for device failed"
+adb_sh ls -d /sys/module/overlay </dev/null || die "overlay module not present"
+adb_su ls /sys/module/overlay/parameters/override_creds </dev/null ||
+  die "overlay module can not be used on ANDROID"
+adb_root &&
+  adb_wait &&
+  D=`adb disable-verity 2>&1` ||
+    die "setup for overlay"
+echo "${D}"
+if [ X"${D}" != X"${D##*using overlayfs}" ]; then
+  echo "${GREEN}[       OK ]${NORMAL} using overlayfs" >&2
+fi
+if adb_sh ls -d /data/overlay </dev/null >/dev/null 2>&1; then
+  echo "/data/overlay setup, clearing out" >&2
+  adb_sh rm -rf /data/overlay </dev/null ||
+    die "/data/overlay removal"
+fi
+adb_sh ls -d /cache/overlay </dev/null >/dev/null 2>&1 ||
+  adb_sh ls -d /mnt/scratch/overlay </dev/null >/dev/null 2>&1 ||
+  die "overlay directory setup"
+adb_reboot &&
+  adb_wait &&
+  adb_sh df -k </dev/null | head -1 &&
+  adb_sh df -k </dev/null | grep "^overlay " &&
+  adb_sh df -k </dev/null | grep "^overlay .* /system\$" >/dev/null ||
+  echo "${ORANGE}[  WARNING ]${NORMAL} overlay takeover before remount not complete" >&2
+
+adb_root &&
+  adb_wait &&
+  adb remount &&
+  adb_sh df -k </dev/null | head -1 &&
+  adb_sh df -k </dev/null | grep "^overlay " &&
+  adb_sh df -k </dev/null | grep "^overlay .* /system\$" >/dev/null ||
+  die  "overlay takeover after remount"
+!(adb_sh grep "^overlay " /proc/mounts </dev/null | grep " overlay ro,") &&
+  !(adb_sh grep " rw," /proc/mounts </dev/null |
+  skip_administrative_mounts) ||
+    die "remount overlayfs missed a spot"
+
+adb_su "sed -n '1,/overlay \\/system/p' /proc/mounts" </dev/null |
+  skip_administrative_mounts |
+  grep -v ' \(squashfs\|ext4\|f2fs\) ' &&
+  echo "${ORANGE}[  WARNING ]${NORMAL} overlay takeover after first stage init" >&2 ||
+  echo "${GREEN}[       OK ]${NORMAL} overlay takeover in first stage init" >&2
+
+# Check something
+A="Hello World! $(date)"
+echo "${A}" | adb_sh "cat - > /system/hello"
+echo "${A}" | adb_sh "cat - > /vendor/hello"
+B="`adb_cat /system/hello`" ||
+  die "sytem hello"
+check_eq "${A}" "${B}" system before reboot
+B="`adb_cat /vendor/hello`" ||
+  die "vendor hello"
+check_eq "${A}" "${B}" vendor before reboot
+adb_reboot &&
+  adb_wait &&
+  B="`adb_cat /system/hello`" ||
+  die "re-read system hello after reboot"
+check_eq "${A}" "${B}" system after reboot
+# Only root can read vendor if sepolicy permissions are as expected
+B="`adb_cat /vendor/hello`" &&
+  die "re-read vendor hello after reboot w/o root"
+check_eq "cat: /vendor/hello: Permission denied" "${B}" vendor after reboot w/o root
+adb_root &&
+  adb_wait &&
+  B="`adb_cat /vendor/hello`" ||
+  die "re-read vendor hello after reboot"
+check_eq "${A}" "${B}" vendor after reboot
+adb remount &&
+  adb_sh rm /system/hello /vendor/hello </dev/null ||
+  die "cleanup hello"
+B="`adb_cat /system/hello`" &&
+  die "re-read system hello after rm"
+check_eq "cat: /system/hello: No such file or directory" "${B}" after flash rm
+B="`adb_cat /vendor/hello`" &&
+  die "re-read vendor hello after rm"
+check_eq "cat: /vendor/hello: No such file or directory" "${B}" after flash rm
+
+echo "${GREEN}[  PASSED  ]${NORMAL} adb remount" >&2