Robolectric is the industry-standard unit testing framework for Android. With Robolectric, your tests run in a simulated Android environment inside a JVM, without the overhead and flakiness of an emulator. Robolectric tests routinely run 10x faster than those on cold-started emulators.

Robolectric supports running unit tests for 15 different versions of Android, ranging from Lollipop (API level 21) to V (API level 35).

Here's an example of a simple test written using Robolectric:

@RunWith(AndroidJUnit4.class)
public class MyActivityTest {

  @Test
  public void clickingButton_shouldChangeResultsViewText() {
    Activity activity = Robolectric.setupActivity(MyActivity.class);

    Button button = (Button) activity.findViewById(R.id.press_me_button);
    TextView results = (TextView) activity.findViewById(R.id.results_text_view);

    button.performClick();
    assertThat(results.getText().toString(), equalTo("Testing Android Rocks!"));
  }
}

For more information about how to install and use Robolectric on your project, extend its functionality, and join the community of contributors, please visit robolectric.org.

If you'd like to start a new project with Robolectric tests, you can refer to deckard (for either Maven or Gradle) as a guide to setting up both Android and Robolectric on your machine.

testImplementation "junit:junit:4.13.2"
testImplementation "org.robolectric:robolectric:4.14.1"

Robolectric is built using Gradle. Both Android Studio and IntelliJ can import the top-level build.gradle.kts file and will automatically generate their project files from it.

To get Robolectric up and running on your machine, check out this guide.

To get a high-level overview of Robolectric's architecture, check out robolectric.org.

Robolectric is actively developed in several locations. The primary location is this GitHub repository, which is considered the source-of-truth for Robolectric code. It is where contributions from the broader Android developer community occur. There is also an active development tree of Robolectric internally at Google, where contributions from first-party Android developers occur. By having a development tree of Robolectric internally at Google, it enables first-party Android developers to more efficiently make contributions to Robolectric. This tree is synced directly to the google branch every time a change occurs using the Copybara code sync tool. Bidirectional merges of this branch and the master branch occur regularly.

Robolectric also has usage in the Android platform via the external/robolectric repo project. Contributions to this source tree are typically related to new SDK support and evolving platform APIs. Changes from this branch are upstreamed to the internal Robolectric tree at Google, which eventually propagate to the GitHub branches.

Although complex, this distributed development model enables Android developers in different environments to use and contribute to Robolectric, while allowing changes to eventually make their way to public Robolectric releases.

If you would like to live on the bleeding edge, you can try running against a snapshot build. Keep in mind that snapshots represent the most recent changes on the master and may contain bugs.

repositories {
    maven { url "https://oss.sonatype.org/content/repositories/snapshots" }
}

dependencies {
    testImplementation "org.robolectric:robolectric:4.15-SNAPSHOT"
}