Espresso

Detailed explanation

Espresso is a powerful UI testing framework developed by Google for Android applications. It's part of the Android Jetpack library and is specifically designed to create reliable and automated UI tests. Unlike other UI testing frameworks that might struggle with synchronization issues, Espresso excels at ensuring that UI interactions happen only when the application is in an idle state. This eliminates flakiness and makes tests more predictable.

Key Features and Benefits:

• Automatic Synchronization: Espresso automatically synchronizes test actions with the UI thread. It waits for the UI to become idle before performing actions, which significantly reduces the chances of tests failing due to timing issues. This is achieved through the IdlingResource interface, which allows Espresso to monitor background tasks and UI updates.
• Concise and Readable Syntax: Espresso uses a fluent API that makes tests easy to read and write. The syntax is designed to mimic user interactions, making the tests more understandable and maintainable.
• White-Box Testing: Espresso is a white-box testing framework, meaning it has access to the internal state of the application. This allows for more precise and targeted testing.
• Integration with Android Studio: Espresso is fully integrated with Android Studio, providing a seamless testing experience. You can easily create, run, and debug Espresso tests directly from the IDE.
• Part of Android Jetpack: Being part of Android Jetpack ensures that Espresso is actively maintained and updated with the latest Android features and best practices.

Practical Implementation:

To start using Espresso, you need to add the necessary dependencies to your build.gradle file:

dependencies {
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'
    androidTestImplementation 'androidx.test:runner:1.5.2'
    androidTestImplementation 'androidx.test:rules:1.5.0'
    androidTestImplementation 'androidx.test.ext:junit:1.1.5'
}

Make sure to also configure the testInstrumentationRunner in your build.gradle file:

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

A basic Espresso test typically involves three main components:

1. onView(): This is used to locate a specific UI element on the screen. You can use various ViewMatchers to identify the element, such as withId(), withText(), withClassName(), and withContentDescription().
2. perform(): This is used to perform an action on the located UI element. Common actions include click(), typeText(), scrollTo(), and swipeLeft().
3. check(): This is used to assert that the UI element is in a specific state. You can use various ViewAssertions to verify the state, such as matches(), doesNotExist(), and isDisplayed().

Here's a simple example of an Espresso test that clicks a button and verifies that the text in a TextView changes:

import androidx.test.ext.junit.runners.AndroidJUnit4;
import androidx.test.rule.ActivityTestRule;
import org.junit.Rule;
import org.junit.Test;
import org.junit.runner.RunWith;
 
import static androidx.test.espresso.Espresso.onView;
import static androidx.test.espresso.action.ViewActions.click;
import static androidx.test.espresso.assertion.ViewAssertions.matches;
import static androidx.test.espresso.matcher.ViewMatchers.withId;
import static androidx.test.espresso.matcher.ViewMatchers.withText;
 
@RunWith(AndroidJUnit4.class)
public class ExampleInstrumentedTest {
 
    @Rule
    public ActivityTestRule<MainActivity> activityRule =
            new ActivityTestRule<>(MainActivity.class);
 
    @Test
    public void testButtonClick() {
        // Locate the button with the ID "button" and click it
        onView(withId(R.id.button)).perform(click());
 
        // Verify that the TextView with the ID "textView" now displays the text "Hello, Espresso!"
        onView(withId(R.id.textView)).check(matches(withText("Hello, Espresso!")));
    }
}

Best Practices:

• Use meaningful ViewMatchers: Choose the most specific and reliable ViewMatchers to locate UI elements. Avoid using generic matchers that might match multiple elements. For example, prefer withId() over withClassName() when possible.
• Keep tests small and focused: Each test should focus on a single specific scenario. This makes tests easier to understand, maintain, and debug.
• Use IdlingResource for asynchronous operations: If your application performs asynchronous operations, use IdlingResource to ensure that Espresso waits for these operations to complete before proceeding with the test. This prevents flakiness caused by timing issues.
• Avoid using Thread.sleep(): Using Thread.sleep() in Espresso tests is generally discouraged because it can make tests slow and unreliable. Instead, rely on Espresso's automatic synchronization mechanisms or use IdlingResource for asynchronous operations.
• Use Page Object Model (POM): The Page Object Model is a design pattern that helps to organize UI tests by encapsulating the UI elements and interactions of each page in a separate class. This makes tests more maintainable and reusable.
• Run tests on a variety of devices and emulators: To ensure that your application works correctly on different devices and screen sizes, run your Espresso tests on a variety of devices and emulators.

Common Tools and Libraries:

• Android Studio: The official IDE for Android development, which provides excellent support for Espresso testing.
• JUnit: A popular unit testing framework for Java, which is used to structure and run Espresso tests.
• Mockito: A mocking framework for Java, which can be used to mock dependencies in Espresso tests.
• Barista: A lightweight Espresso extension library that provides a more concise and readable syntax for common UI testing tasks.
• Kakao: Another Kotlin-based DSL that simplifies writing Espresso tests with a more expressive and readable syntax.

Espresso is a robust and reliable UI testing framework that can help you create high-quality Android applications. By following the best practices and using the available tools and libraries, you can write effective and maintainable UI tests that ensure your application works correctly and provides a great user experience.

Further reading

• Espresso Documentation
• Android Testing Codelab
• Barista Library
• Kakao Library