TDD and mobile development: some forgotten techniques, illustrated with Android

TDD and mobile:
some forgotten techniques!
Matteo Vaccari
mvaccari@thoughtworks.com

Deliver valuable
software faster

Deliver valuable
software faster,
sustainably

WHY TEST?
• Tests help me design my code
• Tests check that my code works
the developer perspective
the tester perspective

Some tests are less
useful than others…

TDD and mobile development: some forgotten techniques, illustrated with Android

Bureaucratic tests
1. Think a line of production code
2. Write a test that proves that the line of code exists
3. Write the line of code
4. .

Useful tests
1. Think a behaviour that I would like to have
2. Write a test that proves that the behaviour exists
3. Experiment ways to pass the test
4. $$$!………… Value !!!

From Growing Object-Oriented Software by Nat Pryce and Steve Freeman

Why is it difﬁcult to
TDD on Android?

ﬁxing Gradle builds
is waste
and is not fun
How do you tell if an activity is value adding or waste?
Imagine doing that activity all the time… how does it feel?
What would the customer say if you do it all the time?

Programming
Skill
> Fancy
Libraries

Model-View Separation
App
(Android)
Core
(Pure Java)
Acceptance
Test
Unit
Test

Unit Doctor Acceptance Tests
public void testInchesToCentimeters() throws Throwab
givenTheUserSelectedConversion("in", "cm");
whenTheUserEnters("2");
thenTheResultIs("2.00 in = 5.08 cm");
}
public void testFahrenheitToCelsius() throws Throwab
givenTheUserSelectedConversion("F", "C");
thenTheResultIs("50.00 F = 10.00 C");
}
public void testUnknownUnits() throws Throwable {
givenTheUserSelectedConversion("ABC", "XYZ");
thenTheResultIs("I don't know how to convert this"
}

public class UnitConversionAcceptanceTest extends ActivityInstrumentationTestCase2<M
public UnitConversionAcceptanceTest() {
super(MainActivity.class);
}
public void testInchesToCentimeters() throws Throwable {
givenTheUserSelectedConversion("in", "cm");
thenTheResultIs("2.00 in = 5.08 cm");
}
private void givenTheUserSelectedConversion(String fromUnit, String toUnit) throws
setText(R.id.fromUnit, fromUnit);
setText(R.id.toUnit, toUnit);
}
private void whenTheUserEnters(String inputNumber) throws Throwable {
setText(R.id.inputNumber, inputNumber);
}
private void thenTheResultIs(String expectedResult) {
assertEquals(expectedResult, getField(R.id.result).getText());
}
private void setText(final int id, final String text) throws Throwable {
final TextView field = getField(id);
runTestOnUiThread(new Runnable() {

}
private void givenTheUserSelectedConversion(String fromUnit, String toUnit) throws
setText(R.id.fromUnit, fromUnit);
setText(R.id.toUnit, toUnit);
}
private void whenTheUserEnters(String inputNumber) throws Throwable {
setText(R.id.inputNumber, inputNumber);
}
private void thenTheResultIs(String expectedResult) {
assertEquals(expectedResult, getField(R.id.result).getText());
}
private void setText(final int id, final String text) throws Throwable {
final TextView field = getField(id);
runTestOnUiThread(new Runnable() {
@Override
public void run() {
field.setText(text);
}
});
}
private TextView getField(int id) {
return (TextView) getActivity().findViewById(id);
}
}

The simplest thing
public class MyActivity extends Activity implements View.OnKeyListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my);
getEditText(R.id.inputNumber).setOnKeyListener(this);
getEditText(R.id.fromUnit).setOnKeyListener(this);
getEditText(R.id.toUnit).setOnKeyListener(this);
}
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
String input = getEditText(R.id.inputNumber).getText();
String fromUnit = getEditText(R.id.fromUnit).getText();
String toUnit = getEditText(R.id.toUnit).getText();
getEditText(R.id.result).setText(" Hello! " + input + fromUnit + toUnit);
return false;
}
private EditText getEditText(int id) {
return (EditText) findViewById(id);
}

The simplest thing
public class MyActivity extends Activity implements View.OnKeyListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my);
getEditText(R.id.inputNumber).setOnKeyListener(this);
getEditText(R.id.fromUnit).setOnKeyListener(this);
getEditText(R.id.toUnit).setOnKeyListener(this);
}
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
String input = getEditText(R.id.inputNumber).getText();
String fromUnit = getEditText(R.id.fromUnit).getText();
String toUnit = getEditText(R.id.toUnit).getText();
getEditText(R.id.result).setText(new UnitDoctor().convert(input, fromUnit, toUnit));
return false;
}
private EditText getEditText(int id) {
return (EditText) findViewById(id);
}

Very easy to test
public class UnitDoctorTest {
@Test
public void convertsInchesToCentimeters() {
UnitDoctor unitDoctor = new UnitDoctor();
assertEquals("2.54", unitDoctor.convert("1", "in", "cm"));
}
}

Yes yes… but my app
interacts heavily with
Android widgets!

Presenter-First
public class UnitDoctorTest {
@Rule public JUnitRuleMockery context = new JUnitRuleMockery()
UnitDoctorView view = context.mock(UnitDoctorView.class);
UnitDoctor unitDoctor = new UnitDoctor(view);
@Test
public void convertInchesToCm() throws Exception {
context.checking(new Expectations() {{
allowing(view).inputNumber(); will(returnValue(1.0));
allowing(view).fromUnit(); will(returnValue("in"));
allowing(view).toUnit(); will(returnValue("cm"));
oneOf(view).showResult(2.54);
}});
unitDoctor.convert();
}

What are mocks good for?
Mocking Android APIs?
Discovering interfaces ✅

Discover the “view” interface
public interface UnitDoctorView {
double inputNumber();
String fromUnit();
String toUnit();
void showResult(double result);
}

@Test
public void showsConversionNotSupported() throws Exception {
context.checking(new Expectations() {{
allowing(view).inputNumber(); will(returnValue(anyDouble()));
allowing(view).fromUnit(); will(returnValue("XYZ"));
allowing(view).toUnit(); will(returnValue("ABC"));
oneOf(view).showConversionNotSupported();
}});
unitDoctor.convert();
}

public interface UnitDoctorView {
double inputNumber();
String fromUnit();
String toUnit();
void showResult(double result);
void showConversionNotSupported();
}

Implement the “view”
interface
• In the Activity class
• In an Android View class
• In a new POJO class

Yes, yes, yes… but my
app interacts heavily with
Android APIs!

Acceptance tests
• Single touch. Dragging the ﬁnger should produce
a colored trail that fades to nothing
• Two touches. Dragging two ﬁngers should
produce two decaying trails
• Multi-touch dashes. Draw a pattern like 
—— —-— —-— 
———————————

Start with a spike!
public class FingerView extends View {
@Override
protected void onDraw(Canvas canvas) {
Paint paint = new Paint();
paint.setColor(Color.BLUE);
paint.setStrokeWidth(3);
paint.setStyle(Paint.Style.STROKE);
canvas.canvas.drawLine(100, 100, 200, 200, paint);
}
}

More spike!
public class MyView extends View {
List<Point> points = new ArrayList<Point>();
@Override
protected void onDraw(Canvas canvas) {
Paint paint = new Paint();
for (int i=1; i<points.size(); i++) {
Point from = points.get(i-1);
Point to = points.get(i);
canvas.drawLine(from.x, from.y, to.x, to.y, paint);
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getActionMasked();
if (action == MotionEvent.ACTION_DOWN) {
points.clear();
points.add(new Point((int) event.getX(), (int) event.getY()));
} else if (action == MotionEvent.ACTION_MOVE) {
points.add(new Point((int) event.getX(), (int) event.getY()));
}
invalidate();
return true;
}
}

FairyFingers
Core
Android
MotionEvent
Android
Canvas
FairyFingersView
onDraw(Canvas) { ... }
onTouchEvent(MotionEvent) { ... }
Android dependent
Pure Java

FairyFingers
Core
Android
MotionEvent
Android
Canvas
FairyFingersView
onDraw(Canvas) { ... }
onTouchEvent(MotionEvent) { ... }
Core
Canvas
Core
MotionEvent
Android dependent
Pure Java

public class FairyFingersCoreTest {
FairyFingersCore core = new FairyFingersCore();
@Test
public void noLinesAtStart() throws Exception {
assertEquals(0, core.lines().size());
}
@Test
public void startOneLine() throws Exception {
core.onTouch(down(10.0f, 100.0f));
assertEquals(1, core.lines().size());
assertEquals("(10.0,100.0)", core.lines(0).toString());
}
@Test
public void oneLineDownMove() throws Exception {
core.onTouch(move(20.0f, 120.0f));
assertEquals("(10.0,110.0)->(20.0,120.0)->(30.0,130.0)", core.lines(0).toString());
}
@Test
public void oneLineDownMoveUp() throws Exception {
TDD!

@Override
public boolean onTouchEvent(final MotionEvent event) {
core.onTouch(new CoreMotionEvent() {
@Override
public int getPointerCount() {
return event.getPointerCount();
}
@Override
public int getPointerId(int pointerIndex) {
return event.getPointerId(pointerIndex);
}
@Override
public void getPointerCoords(int pointerIndex, CorePoint outPointerCoords) {
MotionEvent.PointerCoords coords = new MotionEvent.PointerCoords();
event.getPointerCoords(pointerIndex, coords);
outPointerCoords.x = coords.x;
outPointerCoords.y = coords.y;
}
@Override
public int getActionIndex() {
return event.getActionIndex();
}
@Override
public int getAction() {

public interface CoreCanvas {
void drawLine(float startX, float startY, float stopX, float stopY);
}
@Override
protected void onDraw(final Canvas canvas) {
for (Line line : core.lines()) {
line.drawOn(new CoreCanvas() {
@Override
public void drawLine(float startX, float startY, float stopX, float stopY) {
canvas.drawLine(startX, startY, stopX, stopY, paint);
}
});
}
}

public interface CoreMotionEvent {
int getAction();
int getPointerCount();
int getPointerId(int pointerIndex);
void getPointerCoords(int pointerIndex, CorePoint outPointerCoords);
}
// Constants copied from android.view.MotionEven
static final int ACTION_DOWN = 0;
static final int ACTION_UP = 1;
static final int ACTION_MOVE = 2;
static final int ACTION_CANCEL = 3;
static final int ACTION_POINTER_DOWN = 5;
static final int ACTION_POINTER_UP = 6;

References
TDD For Android book (unﬁnished!) leanpub.com/tddforandroid
Source code for examples: github.com/xpmatteo
These slides are on slideshare.net/xpmatteo
Learn OOP and TDD well: 
Growing Object-Oriented Software, Nat Pryce and Steve Freeman 
TDD By Example, Kent Beck 
Applying UML and Patterns, Craig Larman

Credits
• Carlo Bellettini was my sparring partner for this work
• The motto “Deliver valuable software faster, sustainably” is
my elaboration on Dan North’s “The goal of software
delivery is to minimise the lead time to business impact.
Everything else is detail.” I advise to attend one of Dan’s
seminars. They are illuminating.
• The “Fairy Fingers” idea is from “Ribbons” by Carlo Pescio
(www.aspectroid.com)
• The “gravity test” example is derived from a presentation
by Diego Torres Milano

Questions?
THANK YOU
WE’RE HIRING!

TDD and mobile development: some forgotten techniques, illustrated with Android

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