Resolving UIAutomator 1.0 NoClassDefFoundError on Android R Emulator

Background : Android Studio 3.6 introduces an Android R preview emulator with ARM support, but executing UIAutomator 1.0 scripts on this emulator triggers incompatibility errors.

Exception details : The test runner prints a deprecation warning and then throws a java.lang.NoClassDefFoundError: Landroid/test/RepetitiveTest with a full stack trace, as shown below.

Warning: This version of UI Automator is deprecated. New tests should be written using UI Automator 2.0 which is available as part of the Android Testing Support Library.
See https://developer.android.com/training/testing/ui-testing/uiautomator-testing.html for more details.
INSTRUMENTATION_STATUS: stream=
Test results for WatcherResultPrinter=Test run aborted due to unexpected exception: Failed resolution of: Landroid/test/RepetitiveTest;
java.lang.NoClassDefFoundError: Failed resolution of: Landroid/test/RepetitiveTest;
    at com.android.uiautomator.testrunner.UiAutomatorTestRunner$WatcherResultPrinter.startTest(UiAutomatorTestRunner.java:297)
    at junit.framework.TestResult.startTest(TestResult.java:168)
    ... (additional stack frames) ...
Caused by: java.lang.ClassNotFoundException: android.test.RepetitiveTest
    ... 10 more
Time: 0.039
OK (1 test)
INSTRUMENTATION_STATUS: shortMsg=Failed resolution of: Landroid/test/RepetitiveTest;
INSTRUMENTATION_STATUS_CODE: -1

Analysis of the stack trace : The error originates in

com.android.uiautomator.testrunner.UiAutomatorTestRunner$WatcherResultPrinter.startTest

, where the missing android.test.RepetitiveTest class is first referenced, causing the NoClassDefFoundError.

Root cause : Android R removed the android.test.base library, which UIAutomator 1.0 relies on. Consequently, the framework cannot locate the RepetitiveTest interface, leading to failure before any test case is executed.

Workaround / Solution : For projects that must continue using UIAutomator 1.0, start a Java process with app_process, manually initialize the UIAutomator test service, and then run UIAutomator 1.0 APIs. This approach requires manually managing test execution order because JUnit3 features are unavailable.

Further reading : Detailed implementation and principles of UIAutomator can be found in the article "Uiautomator 项目搭建与实现原理" (https://testerhome.com/articles/20078).