The Hitchhiker’s guide to Android Testing, part 2: Espresso

April 03, 2015

by W.Elsinga

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As mentioned in the first article Ali Derbane and me wrote about Android Functional Testing, there are a lot of frameworks you can use. In this second part of the journey I will be explaining the functional testing framework called Espresso.

Introduction

Introduced at the GTAC in 2013, Espresso is designed to be used in environments where the developers write their own tests, and makes it possible to write concise, beautiful, and reliable Android UI tests quickly.
Espresso has several general components:

The Espresso class offers the onView and onData methods which, alone, can be used for a good numbers of possible tests on a given interface.
ViewMatchers contains a collection of objects that implements the interface Matcher <? super View>. Using this Class you can collect and check View elements. For example, getting a View element (Button) with text “7”.
ViewActions contains a collection of viewAction objects to perform actions on a view. These actions are passed to the method ViewInteraction.perform and may contain multiple actions. For example, clicking on a View element (Button).
ViewAssertions contains a collection of ViewAssertion to conduct checks on views.

To illustrate these components a test can look like this:

Espresso.onView(ViewMatchers.withText("7")).perform(ViewActions.click());
Espresso.onView(withId(R.id.result)).check(ViewAssertions.matches(ViewMatchers.withText("42")));

And the good news, as of last year Google has introduced a Testing Support Library containing Espresso. So lets start by implementing Espresso.

To illustrate, we are going to write some tests that tests agains a Android calculator application. The common test scenario we will be implementing is testing if ‘6’ x ‘7’ equals ‘42’.

Define the test runner

To use Espresso we first need to define who is running the tests. Espresso uses a new runner named AndroidJUnitRunner. This runner, based on InstrumentationTestRunner and GoogleInstrumentationTestRunner, runs JUnit3 and JUnit4 tests against your Android application.

First add the dependencies to your build.gradle, assuming you have installed the Testing Support Library.

dependencies {
androidTestCompile 'com.android.support.test:testing-support-lib:0.1'
}

Then add the runner in your build.gradleandroid.defaultConfig configuration:

defaultConfig {
...
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}

Writing the test

As you may know test classes must be in src\androidTest\com.example.package.tests, com.example.package being the package specified in the package attribute of the manifest element in the AndroidManifest file.
Also each test class must extend the abstract class ActivityInstrumentationTestCase2 and supply the Test Activity as generic type that will be used by default for testing.
It must also be passed to the superclass via the super(). To make the Test Activity being called by the test framework, simply define a setup which calls the synchronous method getActivity().

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public class FunctionalInstrumentationTest extends ActivityInstrumentationTestCase2<ActivityToTest> {

public FunctionalInstrumentationTest() {
super(ActivityToTest.class);
}

@Override
protected void setUp() throws Exception {
super.setUp();
getActivity();
}
}

As mentioned we want to check if ‘6’ x ‘7’ equals ‘42’.

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public void testAnswer_to_the_Ultimate_Question_of_Life_the_Universe_and_Everything() {
onView(withText("7")).perform(click());
onView(withText("×")).perform(click());
onView(withText("6")).perform(click());
onView(withText("=")).perform(click());

onView(withId(R.id.resText)).check(matches(withText("42")));
}

You may have noticed, this example is using static imports. This is solely done to make the code more readable.

Other actions you want to use are:

pressBack(); to simulate the use of the “back” button,
isDisplayed(); to check if an element is being shown and
scrollTo(); to scroll to an element.

Running the test

Now lets do the fun part, lets run the test. This can be done from the command line with he command line with gradle connectedAndroidTest or using Android Studio by:

Open Run menu | Edit Configurations
Add a new Android Tests configuration
Choose the module you are testing
Define our test runner: android.support.test.runner.AndroidJUnitRunner

So now you know a bit more about Espresso. If you want to know more, you may want to visit:

Updated (08-04) When running the tests with gradle you can just use gradle connectedAndroidTest

The Hitchhiker’s guide to Android Testing, part 2: Espresso

Introduction

Define the test runner

Writing the test

Running the test

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