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Espresso is a UI automation library for Android maintained by Google and has become the defacto standard to write android UI tests. The core API is concise and simple however sometimes wrapping your head around its nitty-gritties could prove to be a challenge if you don’t live and breathe android day in and day out.

With this series, I’m hoping to change that. We’ll approach espresso from the perspective of an n00b engineer (I.e. a beginner trying to get familiar and most importantly start) and try to deconstruct what it means to write effective and scalable Android UI automation.

We have lots of interesting capabilities to explore and I’m super excited to start this journey along with you.

Let’s start, shall we?

Why espresso?

If you’ve had previous experience with E2E Automation with Appium or other tools, you may be asking why we should bother to learn a new automation API?

Why not just use Appium espresso driver and use a well-learned API (compatible with Selenium Webdriver W3C spec nonetheless)?

And you certainly have a point. In certain contexts , Appium is a great tool.

However, one of the biggest reasons to prefer Espresso is a combination of technical and human factors, some of these are listed below:

• Tests under app codebase: The tests are written within your app codebase and have dedicated tooling support within Android studio, the IDE that android devs use day in and day out. This goes a long way in reducing the inertia and friction that you may face if you try to onboard devs to write functional E2E tests in another repo. I’ve tried this in the past and it’s not always the most intuitive Dev workflow.
• Dev don’t need to learn a new language: You can write tests in Kotlin or Java, the language android devs are already familiar with and they don’t have to pick up a new language, thus there is less friction in getting devs to write tests. In Agile teams with horribly skewed Test to Dev ratios, this could be the difference in encouraging a whole team approach to quality.
• Both black and white box tests: Espresso supports writing black-box UI automation but also has white box access to android code and thus offers a lot of power in the hands of the test author since they can leverage knowing source code internals to write better and targeted tests.
• Access to Instrumentation: Tests have access to instrumentation from android and espresso does a lot of synchronization checks behind the scenes like checking the message queue is empty and there is no background Async processing happening. This is great since you can skip ineffective polling logic and let espresso take care of it.
• Community support: It’s maintained by Google thus you can be sure of dedicated communicated support and enhancements and bug fixes making their way into future versions.
• And many more … We can go on and on.

Hopefully, you get the drift and see the possibilities, and are excited to learn it with me.

Talk is cheap, show me the code!

I’m glad you are as eager as me. Let’s start

Setting up

We’ll use Android Studio as our main IDE (Integrated development environment). You can download it fromGoogle’s website and install it on your machine and platform following the instructions on the site.

We would use example apps already provided by Google engineers in their open-source GitHub repo*testing-samples* repo under android.

We will use a forked version of this repo to ensure the codebase does not change much, however feel free to fork your own version if it helps.

These examples are well written with an app and example espresso tests that we’ll draw inspiration from to understand espresso API.

For our first example we’ll useBasicSamplerepo.

Setting up dependencies

We’ll need to add the below dependencies to our build.gradle file.

Remember we’ll use the app/build.gradle file and not the root level file

androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
androidTestImplementation 'androidx.test:runner:1.4.0'
androidTestImplementation 'androidx.test:rules:1.4.0'

Also, we’ll set up the test instrumentation runner as AndroidJUnitRunner by adding the below code under defaultConfig

plugins {
  id 'com.android.application'
}

android {
    compileSdkVersion 28

    defaultConfig {
        applicationId "com.my.awesome.app"
        minSdkVersion 15
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
}

dependencies {
    androidTestImplementation 'androidx.test:runner:1.4.0'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}

After adding this, remember to sync the Gradle project in Android studio to ensure the above dependencies are downloaded.

Writing your first android espresso test

For our first hello world test, we’ll open an app screen, perform some UI actions like type and click and then verify if the app is in the desired state with an assertion.

Before we write our first test, lets understand basic component of any espresso test.

A simple test structure

An espresso test at its heart has 3 main components.

Most of these are imported as static methods.

• Matcher - Write a matcher expression that would find an android element. For e.g. Find a View (ListView, RecyclerView, or DataAdapter).
  • Android espresso uses Hamcrest matchers expressions to specify this. If you are not familiar with Hamcrest matchers, don’t worry we’ll understand them more when we look at writing tests.
• Action - Once you find an element, you’ll naturally want to perform some UI action on it like a real user would
  • You could imagine as a user you may want to:
  • Tap on an element or
  • Type some text or
  • Swipe in any allowed direction and so on …
  • Depending on the element Espresso will provide you with methods to specify these actions
• Assertion - Great we found an element and also did an action. Are we done? Not quite. After performing an action, you should assert if the app actually did what you expected it to since a test that does not assert an outcome might give a false positive and miss bugs. Espresso provides Assertion objects depending on the type of element for this.

If you take a step back, this resembles very closely to the arrange-act-assert pattern of writing clean tests. Espresso devs sure did a good job in implementing this neat pattern right into the core API design.

Our first test

With those basics and theories out of the way, we are ready to write our first test.

Let’s understand the flow we want to automate and try it manually first:

1. Open our app under test
2. Launch the MainActivity
3. Find a view with id editTextUserInput
4. Type some text into the above edit text box
5. Close keyboard
6. Find a view with id changeTextBt
7. Click on the above button
8. Verify the label with id textToBeChanged shows the text that we entered

Here is thecomplete test:

@RunWith(AndroidJUnit4.class)
@LargeTest
public class ChangeTextBehaviorTest {

    public static final String STRING_TO_BE_TYPED = "Espresso";

    /**
     * Use {@link ActivityScenarioRule} to create and launch the activity under test, and close it
     * after test completes. This is a replacement for {@link androidx.test.rule.ActivityTestRule}.
     */
    @Rule public ActivityScenarioRule<MainActivity> activityScenarioRule
            = new ActivityScenarioRule<>(MainActivity.class);

    @Test
    public void changeText_sameActivity() {
        // Type text and then press the button.
        onView(withId(R.id.editTextUserInput))
                .perform(typeText(STRING_TO_BE_TYPED), closeSoftKeyboard());
        onView(withId(R.id.changeTextBt)).perform(click());

        // Check that the text was changed.
        onView(withId(R.id.textToBeChanged)).check(matches(withText(STRING_TO_BE_TYPED)));
    }
}

Let’s unpack this:

JUnit annotation

To run any test we use JUnit4 and as such annotate the test class with:

@RunWith(AndroidJUnit4.class)

Optional test size annotation

Google uses annotations to differentiate between different types of tests and UI tests are considered as Large tests (since E2E tests are higher fidelity and take time to run). Simon Stewart (Creator of Selenium Webdriver wrote an excellent blog on this that is worth a readhere)

@LargeTest

Define JUnit rule

Every espresso test starts by starting an Activity (or a screen) that we want to test and this is achieved by defining a JUnit rule like below:

@Rule public ActivityScenarioRule<MainActivity> activityScenarioRule
            = new ActivityScenarioRule<>(MainActivity.class);

If we see this project this only has a single MainActivity and thus we pass that to ActivityScenarioRule class and annotate this with @Rule

Find an element and perform an action

Now for the fun part, we want to find our textbox, enter some text into it and then close the keyboard. Let’s see how this is done in Espresso.

onView(withId(R.id.editTextUserInput)).perform(typeText(STRING_TO_BE_TYPED), closeSoftKeyboard());

• We start with defining that we are interested in finding a View using**onView()** method.
• We then say that we want to find the element using id using withId() and pass it the relevant id, in this case R.id.editTextUserInput, This returns an object of type ViewInteraction and we are ready to perform some action on this
• In this example we want to type some text, we wrap these actions inside:perform() method that (if we look at its signature) takes a list of actions to be performed in sequence

public ViewInteraction perform(final ViewAction... viewActions) {

We can type using: typeText() and pass it a string to type on the keyboard

perform(typeText(STRING_TO_BE_TYPED), closeSoftKeyboard());

And also pass closeSoftKeyboard() to close the keyboard once done.

In similar style, we can click a button by first finding the button and then performing a tap as below:

onView(withId(R.id.changeTextBt)).perform(click());

Finally, as we mentioned a test is incomplete without an assertion.

We’ll check that the text box changes its text based on what we had previously typed using:

onView(withId(R.id.textToBeChanged)).check(matches(withText(STRING_TO_BE_TYPED)));

You can see we find the element using onView() and then use the check()method that takes a ViewAssertion object judging from its signature and returns a ViewInteraction to chain further methods in sequence if needed

public ViewInteraction check(final ViewAssertion viewAssert) {

we specify we want to find check that the element has a text matching what we entered using matches(withText(STRING_TO_BE_TYPED)) and this is a familiar pattern towards writing espresso tests.

Bonus: Cheat sheet

While the above test is a simple example of the most common app actions that we could perform, espresso has a rich API capable of supporting different use cases. We’ll see more of them in subsequent parts of this series. However if you want to glance at the core API, Google devs have provided a friendly cheat sheet that you could viewhere

Conclusion

Hopefully this post gives you an idea on how easy it is to get started with espresso. Stay tuned for next post where we’ll dive into how to automate DataAdapter android controls

As always, Do share this with your friends or colleagues and if you have thoughts or feedback, I’d be more than happy to chat over at twitter or comments. Until next time. Happy Testing and coding.