• No Android Studio/GUI applications required.
• Android emulator runs on a Docker container.
• Accelerates build speed and stablize testing process, especially UI Tests.
• Has ability to cache Gradle distribution and dependencies.

You can either use Gradle Wrapper or Local Installation but first option is recommended because of following reasons.

• Reliable: Different users get the same result on any give gradle version.
• Configurable: Say that to update new gradle version to different users and execution environments (IDE, CI machine, etc), you only need to edit the config file, gradl wrapper will take care the rest.

Gradle wrapper is a script that allow you to run the build with predefined version and settings. These distribution information is stored in gradle/wrapper/gradle-wrapper.properties

To change the version of gradle wrapper, grab one at https://services.gradle.org/distributions/ and update distributionUrl accordingly.

By default all files downloaded under docker container doesn't persist if that container is removed. Therefore, gradle needs to download dependencies for every build, including gradle distribution and app libraries.

To prevent that behavior, Docker offers a solution called Volume. Volumes are typically directories or files on host filesystem and are accessible from both container and host. They will not be removed after the container is wiped out.

The Gradle cached files are by default located under GRADLE_USER_HOME ( / ), so you can keep them there and move to another director. Docker will persist them as long as you define a volume for that directory.

ENV GRADLE_USER_HOME=/cache
VOLUME $GRADLE_USER_HOME

Ok. Looks good, check out these directories to see how things are wired up on host machine:

• On Macos: screen ~/Library/Containers/com.docker.docker/Data/vms/0/tty
• On Linux: under ~/var/lib/docker/volumes

Some useful commands for Docker volume:

• To list all volumes are being use: docker volume ls
• To get detailed information of a specific volume, docker volume inspect [volume_id]

55s instead of 4m 25s for doing the same task. Ok, I have 3 mins to make a cup of coffee ☕☕

You probably see this prompt when booting an ARM-based emulator. They were old and deprecated since Android SDK Level 25. In the contrary, x86 (or x86_64) emulators are 10x faster. However, it requires your host to have hardware acceleration (HAXM on Mac & Windows, QEMU on Linux).

I won't go too detail about architecture defination but focus more on improving the stability and perfomance of Android Emulator when perfoming UI tests.

The script below simply checks whether host system supports Hardware Accelerator and KVM to run x86 emulator rather than ARM.

  cpu_support_hardware_acceleration=$(grep -cw ".*\(vmx\|svm\).*" /proc/cpuinfo)
  kvm_support=$(kvm-ok)

  emulator_name=${EMULATOR_NAME_ARM}
  if [ "$cpu_support_hardware_acceleration" != 0 ] && [ "$kvm_support" != *"NOT"* ]; then
    emulator_name=${EMULATOR_NAME_x86}
  fi

Disable animation when Android emulator is fully loaded and ready to use.

#!/bin/bash

function wait_emulator_to_be_ready() {
  cpu_support_hardware_acceleration=$(grep -cw ".*\(vmx\|svm\).*" /proc/cpuinfo)
  kvm_support=$(kvm-ok)

  emulator_name=${EMULATOR_NAME_ARM}
  if [ "$cpu_support_hardware_acceleration" != 0 ] && [ "$kvm_support" != *"NOT"* ]; then
    emulator_name=${EMULATOR_NAME_x86}
  fi

  adb devices | grep emulator | cut -f1 | while read line; do adb -s $line emu kill; done
  emulator -avd "${emulator_name}" -verbose -no-boot-anim -no-window -gpu off &
  boot_completed=false
  while [ "$boot_completed" == false ]; do
    status=$(adb wait-for-device shell getprop sys.boot_completed | tr -d '\r')
    echo "Boot Status: $status"

    if [ "$status" == "1" ]; then
      boot_completed=true
    else
      sleep 1
    fi
  done
}

function disable_animation() {
  adb shell "settings put global window_animation_scale 0.0"
  adb shell "settings put global transition_animation_scale 0.0"
  adb shell "settings put global animator_duration_scale 0.0"
}

wait_emulator_to_be_ready
sleep 1
disable_animation

Some additional adb commands that helps you avoid flaky tests in some common cases:

# Disable soft keyboard
adb shell settings put secure show_ime_with_hard_keyboard 0
# Set the default locale 
adb shell am broadcast -a com.android.intent.action.SET_LOCALE --es com.android.intent.extra.LOCALE EN

Here are some basic options for faster booting Emulator. Unlikne adb, you can only specify those when starting the emulator, not later on. Consider this command:

emulator -avd ${EMULATOR_NAME} -no-boot-anim -no-window -gpu off -accel auto -memory 2048 -skin 1440x2880

• -no-boot-anim: Disable the boot animation during emulator startup for faster booting
• -acel auto: Determine automatically if acceleration is supported and use it when possible
• -no-window -gpu off: This option is useful when running the emulator on servers that have no display. You'll still be able to access the emulator through adb or the console. UI tests result logs normally.
• -skin 1440x2880: In case you want the screen has enough room of item views, especially with ListView or RecyclerView. Use it at your risk, it's better to handle them properly. You always have customer using small android phone.
• -memory 2048: Specify the physical RAM size from 128 to 4096 MBs, especially suits with high permomance machine. 4GB RAM, why not?

Let's use Sunflower as sample.

Build new Docker Image with name android-container and tag sunflower:

docker build -t android-container:sunflower .

Clone and go to top level directory of Sunflower project:

git clone https://github.com/android/sunflower && cd sunflower/

Mount /sunflower into container as /data, use volume gradle-cache, which is pointed to /cache in the container and run Gradle tasks!

docker run --privileged -it \
--rm -v $PWD:/data \
-v gradle-cache:/cache \
android-container:sunflower \
bash -c '. /start.sh && /data/gradlew test connectedAndroidTest -p /data'

Released under the Apache License.

Read the LICENSE for more details.