One approach to architecture on IOT apps that allows for automated testing

1. Riaan Cornelius
Project Hoptimus – Automating the home brewing process

2. What will we be covering
> Beer brewing 101
> Project Hoptimus
> Challenges when developing IOT solutions
> Clean architecture
> What’s next

3. Beer brewing 101

4. Beer brewing 101
Malting
Mashing
Lautering Boiling
Whirlpooling
Fermenting Conditioning
Filtering
Packaging

5. Beer brewing 101

6. Beer brewing process - simplified
Mashing
• Extracting sugars from malted barley
• Separating wort from grains
Boiling
• Boiling wort
• Adding hops, spices or other additives
Fermenting
• Adding yeast to boiled (and cooled) wort
• Fermenting at a specific temperature until all sugar is converted
Packaging
• Getting beer into some vessel (Bottle or keg usually)
• Enjoy once beer is carbonated

7. Project Hoptimus - Requirements
Recipe
•Import recipe (BeerXML standard)
•Display overview and current brew process
Mashing
•Pump in correct amount of water
•Monitor temperature for mash duration
•Pump wort to boil kettle
Boil
•Boil water for boil duration
•Alarms to add hops / additives
•Pump wort to fermenter once wort is cooled
Ferment
•Monitor and control temperature for duration of fermentation
•Monitor specific gravity to determine when fermentation is done
•Log all measurements to cloud database

8. Challenges when developing IOT applications
> Hardware is difficult to emulate
> Testing physical sensors is hard
> God objects abound in Android
> Behaviour tends to spread across classes

9. Clean Architecture

10. Hexagonal architecture
> Not a silver bullet
> Separates contract from implementation
> Makes code easier to test
> Allows running your IOT app on an emulator

11. Hexagonal Architecture

12. Hexagonal architecture on Android Things
> We need to create a standard Android Things project and make two
simple changes:
1. Add a provided dependency to your build.gradle
2. Add an intent filter to your manifest
> For each service / piece of hardware
1. Create a port (the contract)
2. Create an adapter for a mock implementation
3. Create an adapter for the real implementation

13. Project setup – build.gradle
apply plugin: 'com.android.application'
android {
...
}
dependencies {
...
compileOnly 'com.google.android.things:androidthings:0.7-devpreview'
...
}

14. Project setup – intent filter
<activity android:name=".HomeActivity"
android:label="@string/app_name">
<!-- This allows launching on an emulator -->
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
<!-- This is to launch at boot on AndroidThings -->
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.IOT_LAUNCHER" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>

15. Hardware setup – Port (contract)
public interface TemperatureSensor {
Float read();
void close();
}

16. Hardware setup – Adapter (mock implementation)
public class MockTemperatureSensor implements TemperatureSensor {
private static final String TAG = MockTemperatureSensor.class.getSimpleName();
@Override
public Float read() {
return 23.3F;
}
@Override
public void close() {
Log.d(TAG, "close");
}
}

17. Hardware setup – Adapter (real implementation)
public class BMP280TemperatureSensor implements TemperatureSensor {
private Bmx280SensorDriver driver;
// ...
private Float temperature;
public BMP280TemperatureSensor(Context context) {
// ...
driver = new Bmx280SensorDriver("I2C1");
driver.registerTemperatureSensor();
}
@Override
public Float read() {
return temperature;
}
@Override
public void close() {
// ...
driver.close();
}
private class TemperatureListener implements SensorEventListener { ... }
}

18. Hardware setup – Activity
class TemperatureActivity : Activity() {
private lateinit var temperatureSensor: TemperatureSensor
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_temperature)
temperatureSensor = getTempSensor()
val button = findViewById<Button>(R.id.button)
val text = findViewById<TextView>(R.id.textTemperature)
button.setOnClickListener({ text.text = temperatureSensor.read().toString() })
}
private fun getTempSensor(): TemperatureSensor {
return if (BuildConfig.MOCK_BUILD) {
MockTemperatureSensor()
} else {
BMP280TemperatureSensor(this)
}
}
}

19. Hardware setup – BuildTypes
buildTypes {
release {
minifyEnabled true
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
buildConfigField "boolean", "MOCK_BUILD", "false"
}
debug {
minifyEnabled false
buildConfigField "boolean", "MOCK_BUILD", "true"
}
}

20. Hardware setup – Testing
@LargeTest
@RunWith(AndroidJUnit4.class)
public class TemperatureActivityTest {
@Rule
public ActivityTestRule<TemperatureActivity> mActivityTestRule =
new ActivityTestRule<>(TemperatureActivity.class);
@Test
public void temperatureActivityTest() {
// Click button to read temperature
ViewInteraction button = onView(allOf(withId(R.id.button), withText("Read"),
childAtPosition(childAtPosition(withId(android.R.id.content), 0), 0),
isDisplayed()));
button.perform(click());
// Check temperature was read from port
ViewInteraction textView2 = onView(allOf(withId(R.id.textTemperature),
childAtPosition(childAtPosition(withId(android.R.id.content), 0), 1),
isDisplayed()));
textView2.check(matches(withText("23.3")));
}
}

21. Hardware setup - Testing

22. What’s next?
> Gluing it all together
> More complex sensors
> Google Nearby API to get alarms / reminders on my phone

23. /* THANK YOU*/
Riaan Cornelius
http://riaancornelius.com/
riaan.cornelius@entelect.co.za
@riaancornelius
http://www.devconf.co.za/