Sunday, July 19, 2015

Very bad network simulation for testing of mobile applications [PART 2]

In the previous post we talked about the need for platform independent, scriptable solution for testing of your mobile applications in a poor internet conditions. To complement the theory with something executable, this post will introduce scripts (Debian Linux like), and a guide to setup your own WIFI access point, which would simulate slow, unreliable mobile internet. You will be able to connect with your Android, iOS, Windows, whatever devices and see from your office, how your apps adapt.

This tutorial will be divided into following sections:

  1. Failure when firstly attempting to solve this problem.
  2. Obtaining the right USB WIFI dongle.
  3. Tutorial for creating an AP from your Linux based workstation.
  4. Script for changing the Quality of service (QoS) characteristics of your AP.
  5. Script for setting particular QoS, simulating GRPS, EDGE, 3G, LTE, whatever networks.
  6. Example usage

Failure, when firstly attempting to solve this problem.

My first attempt did not end up successfully. I am not saying it is a wrong way, but I was just not able to go this way. The plan was to:

  • Buy WIFI dongle with ability to be in AP mode.
  • Virtualize OpenWRT (a small Linux distro, usually run on routers) in the VirtualBox.
  • Install on that virtual machine a Cellular-Data-Network-Simulator - which is capable running on OpenWRT, and is established on well known technologies: tc, iptables and CloudShark.
  • Connect with devices to that AP, and use CloudShark to sniff the network in order to see particular packets.
It looked promising. It would be just an integration of already existing parts, not reinventing a wheel. A fairy tail. It worked. Even when I found out that it would require some work to do in order to script the way, how the devices are connected to the Cellular-Data-Network-Simulator, and the way how the QoS characteristics are changed in order to switch among 2G, 3G, etc. networks. But it was nothing impossible to overcome. The biggest problem which I encountered after I set it up, was the stability of the AP. It switched off the WIFI dongle at random intervals. I studied various OpenWRT log files, but have not found the root cause, hence I was not able to fix it. I needed to think out a different way. Following describes my second attempt, which finally worked.

Obtaining the right USB WIFI dongle.

First things first. Before buying the WIFI dongle, checkout its chipset, and see, whether it is supported by some Linux driver. I am using TP-Link TL-W22N. Its chipset AR9271 is supported by ath9k_htc driver.

Tutorial for creating an AP from your Linux based workstation.

Next you will need to setup various things properly: hostapd, DHCP server, firewall. I followed this great post (automated in the install script for Debian like systems here). In that install script, you can also spot a part (wifi_access_point), which would enable you to start the AP as a service.

Script for changing of Quality of service (QoS) characteristics of your AP.

Now, you should be able to connect to the created AP with your devices. It should provide you a similar Internet connection quality as you have on your workstation. To simulate various cellular data networks we need to limit it somehow.

Following script does it by setting various firewall rules. You will need to alter it a bit before using it.
  1. Set IF_IN to network interface name which is dedicated to the created AP.
  2. Set IF_OUT to network interface name by which is your workstation connected the Internet.
  3. Set IP_IN to a IP address space which will be assigned to your connected devices (you chose this when setting up a DHCP server).
  4. Set IP_OUT to the IP address of your application backend server.
Save the following script, and named it e.g.
#  tc uses the following units when passed as a parameter.
#  kbps: Kilobytes per second 
#  mbps: Megabytes per second
#  kbit: Kilobits per second
#  mbit: Megabits per second
#  bps: Bytes per second 
#       Amounts of data can be specified in:
#       kb or k: Kilobytes
#       mb or m: Megabytes
#       mbit: Megabits
#       kbit: Kilobits
#  To get the byte figure from bits, divide the number by 8 bit

# Name of the traffic control command.

# The network interface we're planning on limiting bandwidth.

# IP address of the machine we are controlling
IP_IN=     # Host IP
IP_OUT= #the address of your backend server

# Filter options for limiting the intended interface.
U32_IN="$TC filter add dev $IF_IN protocol ip parent 1: prio 1 u32"
U32_OUT="$TC filter add dev $IF_OUT protocol ip parent 2: prio 1 u32"

start() {
    ping -c 1 $IP_OUT >/dev/null 2>&1
    if [ $? -ne 0 ]; then
 echo "Error:"
        echo "The IP address: $IP_OUT is not reachable!"
 echo "Check out the backend server address!"
 exit -1

    $TC qdisc add dev $IF_IN root handle 1: htb default 30
    # download bandwidth
    $TC class add dev $IF_IN parent 1: classid 1:1 htb rate "$1"
    $U32_IN match ip dst $IP_IN/24 flowid 1:1
    # in delay
    $TC qdisc add dev $IF_IN parent 1:1 handle 10: netem delay "$3" "$4" distribution normal
    # in packet loss
    $TC qdisc add dev $IF_IN parent 10: netem loss "$7" "$8"

    # upload bandwidth
    $TC qdisc add dev $IF_OUT root handle 2: htb default 20
    $TC class add dev $IF_OUT parent 2: classid 2:1 htb rate "$2"
    $U32_OUT match ip dst $IP_OUT/32 flowid 2:1
    # out delay
    $TC qdisc add dev $IF_OUT parent 2:1 handle 20: netem delay "$5" "$6" distribution normal
    $U32_OUT match ip dst $IP_OUT/32 flowid 20:

stop() {

# Stop the bandwidth shaping.
    $TC qdisc del dev $IF_IN root
    $TC qdisc del dev $IF_OUT root

show() {

# Display status of traffic control status.
    echo "Interface for download:"
    $TC -s qdisc ls dev $IF_IN
    echo "Interface for upload:"
    $TC -s qdisc ls dev $IF_OUT


case "$1" in

    if [ "$#" -ne 8 ]; then
        echo "ERROR: Illegal number of parameters"
        echo "Usage: ./ start [downloadLimit] [uploadLimit] [inDelayMax] [inDelayMin] [outDelayMax] [outDelayMin] [packetLossPercentage] "
        echo "[downloadLimit]  See man page of tc command to see supported formats, e.g. 1mbit."
 echo "[uploadLimit] The same as for downloadLimit applies here."
 echo "[inDelayMax] Max delay in miliseconds for requests outgoing from AP."
 echo "[inDelayMin] Min in delay."
 echo "[outDelayMax] Max Delay in miliseconds for requests outgoing to servers."
 echo "[outDelayMin] Min out delay."
 echo "[packetLossPercentage] The percentage of packet lost"
 echo "Example: / 1mbit 1mbit 50ms 20ms 30ms 10ms 5%"
        exit -1

    echo "Starting  shaping quality of service: "
    start $2 $3 $4 $5 $6 $7 $8
    echo "done"


    echo "Stopping shaping quality of service: "
    echo "done"


    echo "Shaping quality of service status for $IF_IN and $IF_OUT:"
    echo ""


    echo "Usage: {start|stop|show}"


exit 0

Script for setting particular QoS, simulating GRPS, EDGE, 3G, LTE, whatever networks.

Now when you have a script to limit the QoS characteristic of your created AP, you will need to do some measurements, in order to have a clue what bandwidth, what latency, and what packet loss various cellular data networks have. You will need to find out a way how to measure these characteristics in the environment where your customers use your application.

The reason is that the same data network type (e.g. 3G) can have different QoS characteristics on different places. There are other factors in play as well: mobile Internet provider, hour of the day, city vs. village, weather and like. For the measurement I used handy mobile applications (for bandwidth and latency) and Fing for a double check up, as it is able to ping any server you like.

Off-topic: Would not be awesome, if there is a web service which would give me the average QoS characteristics of any place in the world for a particular hour of the day, for a particular data carrier, for particular weather and other conditions? I submitted a bachelor thesis assignment, but so far no enrollment :) And it would be IMO quite easy to setup: a mobile application with gamification characteristics to find out the particular statistics, store them, and make them available via some REST endpoints.

Save the following script as, into the same directory as previous script was saved. The measured values, you can see, are valid for average morning in Brno, Czech republic. The average was made after one week of measuring.


echo -n "Shaping WIFI to "

case "$1" in

 echo "GRPRS"
 $QOS stop > /dev/null 2>&1
 $QOS start 80kbit 20kbit 200ms 40ms 200ms 40ms 5%

 echo "EDGE"
 $QOS stop > /dev/null 2>&1
 $QOS start 200kbit 260kbit 120ms 40ms 120ms 40ms 5%

 echo "HDSPA"
 $QOS stop > /dev/null 2>&1
 $QOS start 2400kbit 2400kbit 100ms 100ms 100ms 100ms 5%

 echo "LTE"

 echo "FULL"
 $QOS stop > /dev/null 2>&1

 echo "DISABLED"
 $QOS stop > /dev/null 2>&1
 $QOS start 1kbit 1kbit 5000ms 5000ms 5000ms 5000ms 5%



exit 0

Example usage

So if you followed the steps, you should be able now to:
  1. Start the AP by: service wifi_access_point start.
  2. Simulate e.g. EDGE, by issuing: EDGE
Ideas have no limits. Use these scripts to e.g. stress network test your application (write a bash script which would randomly switch among all types of the network in a random intervals), or use WireShark to go deeper, to see actual packets being transmitted. Your development team would love you, if you attach to your bug report a saved transmission with a packet level information. Fixing of tough, non-deterministic network issues becomes more easy.

Disclaimer: I am still improving the scripts, use them on your own danger :) Any feedback on how you utilized these scripts, or your improvements would be deeply appreciated.

Thursday, June 25, 2015

Very bad network simulation for testing of mobile applications [PART 1]


Mobile internet is a must for smartphones. Most of the apps are somehow connected to the server, syncing every now and then. Whether it is to just show an advertisement, syncing your local changes with your profile somewhere in the cloud or maybe protecting the app from being distributed as cracked one, without paying for it.

But there is also another category of mobile applications, which heavily depend on the Internet connection. One example of such are applications intended for communication. Let's consider for instance PhoneX app.

All its features (secure calls, secure messaging and secure file transfer) require a decent Internet connection to work. But it just begins with its main features, everything from authentication, through contacts presence and server push notifications establish TCP or UDP connections with the servers.

Disadvantages of traditional way

With such applications, QE teams have to devote non-trivial effort to test applications functionality under various network conditions. There are various ways how to simulate real user conditions. Firstly, one can buy SIM cards for all of his devices, enable mobile data and spend lot of time with travelling around city. This method makes the testing environment the most real one, but one has to consider its downsides as well:

  • Out of reach of your computer, its more difficult to automate some of the app routines while you are moving, to offload mundane repeating of interactions with the app. In your office, it would be more easy to setup a script or to write a functional test which would send 200 subsequent messages or so.
  • Quality of service statistics vary around the globe significantly. And you do not have to go so far. For example 3G bandwidth, latency and jitter is quite different in two towns not far away from each other (100 Km). Needles to say that some places can only dream about LTE, and that these QoS characteristics vary also according to day hour (you would not like testing at 1 AM somewhere in the public transportation). Simulating all these different conditions in laboratory would be indeed more efficient.
  • It would be more difficult to intercept the communication e.g. with WireShark. It is sometimes handy, when developers need to see actual transmitted packets, in order to fix the issue.
  • It is more reliable to save mobile system logs such as logcat on Android right to the computer. Do now know why, but it is often the case for me, that some of the logs are missing when saving them to the file on the device (maybe some buffer limitation, who knows). I found more reliable to have phones connected to the computer and save such logs right away there.
  • Total lost of connection, or lost of some of the packets is more easily to be scripted in your testing laboratory, then in the real world.
  • Users use also various WIFI APs, which restrictions (e.g. isolation of clients) can badly affect your application features.
  • The most obvious reason is the time spent while moving out there, comparing with the time spent in the comfort of your air conditioned office furnitured with the most ergonomic seats out there.
For sure there are other reasons, why I consider simulating of poor internet connection to be done in the laboratory as better option than trying to reproduce the bugs outside. Please, I am not saying that it can substitute all testing while you are moving with the device. I am just saying that it can replace most of the testing under various network conditions.

Next part

In the next part we we will look into how to setup a WIFI Access Point, and some scripts which would enable simulating of poor internet connection. iOS platform has a solution for this already (Settings -> Developer -> Network Link Conditioner). Our solution would be platform independent, and would solve all of the disadvantages described above. Stay tuned.

Tuesday, June 2, 2015

Recording tests on Android (neither root, nor KitKat required)

A test suite is good only when provides a good feedback. Testing mobile apps is cumbersome, and far from robust (actually all UI tests are like that). A meaningful test report is inevitable. That is why, I really like to have executions of my tests recorded. Such recordings are great thing to avoid a repeated execution of the test to find out why it failed (repeated execution of tests should be avoided as plague).

It is awesome that Google added a a native support for recording of your Android 4.4.x+ device screen, but what the other folks with lower Android versions. We can not afford to test only on 4.4+, as it is wise to support at least 4.0+. A rooted device is not the answer for me, as we need to test on real devices, devices which are actually used by our customers.

OK, all Android versions are capable to take a screen capture, so why not to use this feature. The following describes small bash scripts, which in simple words create a video (actually a .gif with 2fps) from such screen captures. It is then easy to use them to record your functional UI tests (showcased on Appium tests).

Firstly, the script which takes screenshots until not terminated into a specified directory on your device:

adb -s $1 shell rm -r $DIR > /dev/null 2>&1
adb -s $1 shell mkdir $DIR > /dev/null 2>&1
for (( i=1; ; i++ ))
 name=`date +%s`
 adb -s $1 shell screencap -p "$DIR/$name.png"
You can try it by executing ./ [serialNumberOfDevice].

Secondly, the script which retrieves taken screenshots from devices into your computer, re-sizes them into smaller resolution, and finally creates an animated .gif:

mkdir "$1"
cd "$1"
adb -s $1 pull $DIR_REMOTE
echo "Resizing screenshots to smaller size!"
mogrify -resize 640x480 *.png
echo "Converting to .gif."
convert -delay 50 *.png "$1"-test.gif
echo "Clearing..."
cp "$1"-test.gif ..
cd ..
rm -rf "$1"
Try it by executing ./ [serialNumberOfDevice] [pathToDirectoryIntoWhichSaveScreenshots]. Just to note that it uses the imagemagic and its sub packages.

Here is an example of .gif created by scripts above, while sending encrypted files through the PhoneX app for a secure communication:
So we have some scripts to execute (indeed there are things to improve, a parameter checking etc.). There are various ways how to use them in your tests, all depend on what testing framework you are using, and in what language your tests are written in. We use the Appium, and its Java client. Following shows executing of the first ( script in the beginning of each test class:
public class AbstractTest {
    private Process takeScreenshotsProcess = null;

    protected void setupDevice1() throws Exception {
        takeScreenshotsProcess = startTakingOfScreenshots(DEVICE_1_NAME);
        //for readability omitted Appium API calls to setup device for testing

    protected Process startTakingOfScreenshots(String deviceName) throws Exception {
        String[] cmd = { "sh/", getDeviceSerialNumber(deviceName)};
        return Runtime.getRuntime().exec(cmd);

    public void tearDown() {
        if(takeScreenshotsProcess != null) {
Hopefully the code above is somehow self explanatory. It starts taking of screenshots before Appium API calls prepare a device for a testing (installs APK, etc.). The same pattern can be used for any number of devices.

Next steps are to use the script in the end of your CI job (e.g. Jenkins). I prefer fine granular CI jobs, which are short to execute, to provide a quick feedback. Therefore, each job is a one test (or matrix of tests), and that is why, starting of taking screenshots is done in the @Before method, and terminated in the @After method.

Please, bear in mind, that previous are just examples. They need to be polished and altered to ones needs. Enjoy testing.