diff --git a/.gitignore b/.gitignore
index c47478af..989911a3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -120,3 +120,5 @@ object-server-for-testing/
 tests/realm-object-server/
 vendor/sync
 vendor/sync*
+packager_out.txt
+build.log.*
diff --git a/scripts/reset-simulators.sh b/scripts/reset-simulators.sh
deleted file mode 100755
index 157eb80d..00000000
--- a/scripts/reset-simulators.sh
+++ /dev/null
@@ -1,52 +0,0 @@
-#!/bin/bash
-
-set -o pipefail
-set -e
-
-export REALM_SWIFT_VERSION=3.0.1
-if [[ -z "$DEVELOPER_DIR" ]]; then
-    export DEVELOPER_DIR="$(xcode-select -p)"
-fi
-
-while pgrep -q Simulator; do
-    # Kill all the current simulator processes as they may be from a
-    # different Xcode version
-    pkill Simulator 2>/dev/null || true
-    # CoreSimulatorService doesn't exit when sent SIGTERM
-    pkill -9 Simulator 2>/dev/null || true
-done
-
-# Run until we get a result since switching simulator versions often causes CoreSimulatorService to throw an exception.
-devices=""
-until [ "$devices" != "" ]; do
-    devices="$(xcrun simctl list devices -j || true)"
-done
-
-# Shut down booted simulators
-echo "$devices" | ruby -rjson -e 'puts JSON.parse($stdin.read)["devices"].flat_map { |d| d[1] }.select { |d| d["state"] == "Booted" && d["availability"] == "(available)" }.map { |d| d["udid"] }' | while read udid; do
-    echo "shutting down simulator with ID: $udid"
-    xcrun simctl shutdown $udid
-done
-
-# Erase all available simulators
-echo "erasing simulators"
-echo "$devices" | ruby -rjson -e 'puts JSON.parse($stdin.read)["devices"].flat_map { |d| d[1] }.select { |d| d["availability"] == "(available)" }.map { |d| d["udid"] }' | while read udid; do
-    xcrun simctl erase $udid &
-done
-wait
-
-xcrun simctl boot "iPhone 5" # React Native seems to want to test with this device
-
-if [[ -a "${DEVELOPER_DIR}/Applications/Simulator.app" ]]; then
-    open "${DEVELOPER_DIR}/Applications/Simulator.app"
-fi
-
-# Wait until the boot completes
-echo "waiting for simulator to boot..."
-until xcrun simctl list devices -j | ruby -rjson -e 'exit JSON.parse($stdin.read)["devices"].flat_map { |d| d[1] }.any? { |d| d["availability"] == "(available)" && d["state"] == "Booted" }'; do
-    sleep 1
-done
-
-# Wait until the simulator is fully booted by waiting for it to launch SpringBoard
-xcrun simctl launch booted com.apple.springboard >/dev/null 2>&1 || true
-echo "simulator booted"
\ No newline at end of file
diff --git a/scripts/test.sh b/scripts/test.sh
index 106a67a7..488a68dc 100755
--- a/scripts/test.sh
+++ b/scripts/test.sh
@@ -6,12 +6,20 @@ set -e
 export TEST_SCRIPT=1
 export NPM_CONFIG_PROGRESS=false
 
-TARGET="$1"
-CONFIGURATION="${2:-"Release"}"
-DESTINATION=
+TARGET=$1
+CONFIGURATION=${2:-Release}
+
+IOS_SIM_DEVICE=${IOS_SIM_DEVICE:-} # use preferentially, otherwise will be set and re-exported
+ios_sim_default_device_type=${IOS_SIM_DEVICE_TYPE:-iPhone 5s}
+ios_sim_default_ios_version=${IOS_SIM_OS:-iOS 10.1}
+
 PATH="/opt/android-sdk-linux/platform-tools:$PATH"
 SRCROOT=$(cd "$(dirname "$0")/.." && pwd)
 XCPRETTY=`which xcpretty || true`
+CI_RUN=false
+if [ -n "${JENKINS_HOME}" ]; then
+  CI_RUN=true
+fi
 
 # Start current working directory at the root of the project.
 cd "$SRCROOT"
@@ -44,16 +52,33 @@ stop_server() {
   fi
 }
 
+startedSimulator=false
+log_temp=
+test_temp_dir=
 cleanup() {
   # Kill started object server
-  stop_server
-
-  # Kill all other child processes.
-  pkill -P $$ || true
+  stop_server || true
+  
+  # Quit Simulator.app to give it a chance to go down gracefully
+  if $startedSimulator; then
+    osascript -e 'tell app "Simulator" to quit without saving' || true
+    sleep 0.25 # otherwise the pkill following will get it too early
+  fi
+  
+  # Kill all child processes.
+  pkill -9 -P $$ || true
 
   # Kill react native packager
   pkill node || true
   rm -f "$PACKAGER_OUT" "$LOGCAT_OUT"
+  
+  # Cleanup temp files
+  if [ -n "$log_temp" ] && [ -e "$log_temp" ]; then
+    rm "$log_temp" || true
+  fi
+  if [ -n "$test_temp_dir" ] && [ -e "$test_temp_dir" ]; then
+    rm -rf "$test_temp_dir" || true
+  fi
 }
 
 open_chrome() {
@@ -81,26 +106,116 @@ start_packager() {
 }
 
 xctest() {
-  local dest="$(xcrun simctl list devices | grep -v unavailable | grep -m 1 -o '[0-9A-F\-]\{36\}')"
+  setup_ios_simulator
+  
+  # - Wait until the simulator is fully booted by waiting for it to launch SpringBoard
+  printf "Waiting for springboard to ensure device is ready..."
+  xcrun simctl launch "$IOS_SIM_DEVICE" com.apple.springboard 1>/dev/null 2>/dev/null || true
+  echo "  done"
+  
+  # - Run the build and test
   if [ -n "$XCPRETTY" ]; then
-    LOGTEMP=`mktemp build.log.XXXXXX`
-    trap "rm $LOGTEMP" EXIT
-    xcodebuild -scheme "$1" -configuration "$CONFIGURATION" -sdk iphonesimulator -destination id="$dest" build test 2>&1 | tee "$LOGTEMP" | "$XCPRETTY" -c --no-utf --report junit --output build/reports/junit.xml || {
+    log_temp=`mktemp build.log.XXXXXX`
+    if [ -e "$log_temp" ]; then
+      rm "$log_temp"
+    fi
+    xcrun xcodebuild -scheme "$1" -configuration "$CONFIGURATION" -sdk iphonesimulator -destination name="iPhone 5s" build test 2>&1 | tee "$log_temp" | "$XCPRETTY" -c --no-utf --report junit --output build/reports/junit.xml || {
 	    EXITCODE=$?
         printf "*** Xcode Failure (exit code $EXITCODE). The full xcode log follows: ***\n\n"
-        cat "$LOGTEMP"
+        cat "$log_temp"
         printf "\n\n*** End Xcode Failure ***\n"
         exit $EXITCODE
     }
+    rm "$log_temp"
   else
-    xcodebuild -scheme "$1" -configuration "$CONFIGURATION" -sdk iphonesimulator -destination id="$dest" build test || {
+    xcrun xcodebuild -scheme "$1" -configuration "$CONFIGURATION" -sdk iphonesimulator -destination id="$IOS_SIM_DEVICE" build test || {
 	    EXITCODE=$?
         echo "*** Failure (exit code $EXITCODE). ***"
         exit $EXITCODE
-	}
+	  }
   fi
 }
 
+setup_ios_simulator() {
+  # - Ensure one version of xcode is chosen by all tools
+  if [[ -z "$DEVELOPER_DIR" ]]; then
+    export DEVELOPER_DIR="$(xcode-select -p)"
+  fi
+  
+  # -- Ensure that the simulator is ready
+  
+  if [ $CI_RUN == true ]; then
+	# - Kill the Simulator to ensure we are running the correct one, only when running in CI
+	echo "Resetting simulator using toolchain from: $DEVELOPER_DIR"
+	
+	# Quit Simulator.app to give it a chance to go down gracefully
+	local deadline=$((SECONDS+5))
+	while pgrep -qx Simulator && [ $SECONDS -lt $deadline ]; do
+	  osascript -e 'tell app "Simulator" to quit without saving' || true
+	  sleep 0.25 # otherwise the pkill following will get it too early 
+	done
+	
+	# stop CoreSimulatorService
+	launchctl remove com.apple.CoreSimulator.CoreSimulatorService 2>/dev/null || true
+	sleep 0.25 # launchtl can take a small moment to kill services
+	
+	# kill them with fire
+	while pgrep -qx Simulator com.apple.CoreSimulator.CoreSimulatorService; do
+	  pkill -9 -x Simulator com.apple.CoreSimulator.CoreSimulatorService || true
+	  sleep 0.05
+	done
+	
+	# - Prod `simctl` a few times as sometimes it fails the first couple of times after switching XCode vesions
+	local deadline=$((SECONDS+5))
+	while [ -z "`xcrun simctl list devices 2>/dev/null`" ] && [ $SECONDS -lt $deadline ]; do
+	  : # nothing to see here, will stop cycling on the first successful run
+	done
+    
+    # - Choose a device, if it has not already been chosen
+    local deadline=$((SECONDS+5))
+    while [ -z "$IOS_SIM_DEVICE" ] && [ $SECONDS -lt $deadline ]; do
+      export IOS_SIM_DEVICE=`ruby -rjson -e "puts JSON.parse(%x{xcrun simctl list devices --json})['devices'].each{|os,group| group.each{|dev| dev['os'] = os}}.flat_map{|x| x[1]}.select{|x| x['availability'] == '(available)'}.each{|x| x['score'] = (x['name'] == '$ios_sim_default_device_type' ? 1 : 0) + (x['os'] == '$ios_sim_default_ios_version' ? 1 : 0)}.sort_by!{|x| [x['score'], x['name']]}.reverse![0]['udid']"`
+    done
+    if [ -z "$IOS_SIM_DEVICE" ]; then
+      echo "*** Failed to determine the iOS Simulator device to use ***"
+      exit 1
+    fi
+    
+    # - Reset the device we will be using if running in CI
+    xcrun simctl shutdown "$IOS_SIM_DEVICE" 1>/dev/null 2>/dev/null || true # sometimes simctl gets confused
+    xcrun simctl erase "$IOS_SIM_DEVICE"
+    
+    # - Start the target in Simulator.app
+    # Note: as of Xcode 7.3.1 `simctl` can not completely boot a simulator, specifically it can not bring up backboard, so GUI apps can not run.
+    #       This is fixed in version 8 of Xcode, but we still need the compatibility
+    
+    "$DEVELOPER_DIR/Applications/Simulator.app/Contents/MacOS/Simulator" -CurrentDeviceUDID "$IOS_SIM_DEVICE" & # will get killed with all other children at exit
+    startedSimulator=true
+  
+  else
+  	# - ensure that the simulator is running on a developer's workstation
+    open "$DEVELOPER_DIR/Applications/Simulator.app"
+    
+    # - Select the first device booted in the simulator, since it will boot something for us
+    local deadline=$((SECONDS+10))
+    while [ -z "$IOS_SIM_DEVICE" ] && [ $SECONDS -lt $deadline ]; do
+      export IOS_SIM_DEVICE=`ruby -rjson -e "puts JSON.parse(%x{xcrun simctl list devices --json})['devices'].each{|os,group| group.each{|dev| dev['os'] = os}}.flat_map{|x| x[1]}.select{|x| x['state'] == 'Booted'}[0]['udid']"`
+    done
+    if [ -z "$IOS_SIM_DEVICE" ]; then
+      echo "*** Failed to determine the iOS Simulator device in use ***"
+      exit 1
+    fi
+  fi
+  
+  # Wait until the boot completes
+  printf "  waiting for simulator ($IOS_SIM_DEVICE) to boot..."
+  until ruby -rjson -e 'exit JSON.parse(`xcrun simctl list devices -j `)["devices"].flat_map { |d| d[1] }.any? { |d| d["availability"] == "(available)" && d["state"] == "Booted" }'; do
+    sleep 0.25
+  done
+  echo " done"
+  echo "It will take some time before the simulator is fully ready, continuing on to other work"
+}
+
 # Cleanup now and also cleanup when this script exits.
 cleanup
 trap cleanup EXIT
@@ -135,24 +250,15 @@ case "$TARGET" in
   xctest RealmJS
   ;;
 "react-tests")
-  if ! [ -z "${JENKINS_HOME}" ]; then
-    ${SRCROOT}/scripts/reset-simulators.sh
-  fi
-
   pushd tests/react-test-app
-
   npm install
   open_chrome
   start_packager
 
   pushd ios
-  xctest ReactTestApp || xctest ReactTestApp
+  xctest ReactTestApp
   ;;
 "react-example")
-  if ! [ -z "${JENKINS_HOME}" ]; then
-    ${SRCROOT}/scripts/reset-simulators.sh
-  fi
-
   pushd examples/ReactExample
 
   npm install
@@ -160,7 +266,7 @@ case "$TARGET" in
   start_packager
 
   pushd ios
-  xctest ReactExample || xctest ReactExample
+  xctest ReactExample
   ;;
 "react-tests-android")
   [[ $CONFIGURATION == 'Debug' ]] && exit 0
@@ -210,7 +316,7 @@ case "$TARGET" in
 
   # Change to a temp directory.
   cd "$(mktemp -q -d -t realm.node.XXXXXX)"
-  trap "rm -rf '$PWD'" EXIT
+  test_temp_dir=$PWD # set it to be cleaned at exit
 
   pushd "$SRCROOT/tests"
   npm install
@@ -223,7 +329,7 @@ case "$TARGET" in
 
   # Change to a temp directory.
   cd "$(mktemp -q -d -t realm.node.XXXXXX)"
-  trap "rm -rf '$PWD'" EXIT
+  test_temp_dir=$PWD # set it to be cleaned at exit
 
   pushd "$SRCROOT/tests"
   npm install