I am using Powermock:
`
// androidx
implementation 'androidx.appcompat:appcompat:1.0.2'
implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test:runner:1.1.0'
androidTestImplementation 'androidx.test.ext:junit:1.1.0'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.1'

// power mock
androidTestImplementation group: 'org.powermock', name: 'powermock-module-junit4', version: '2.0.0'
androidTestImplementation group: 'org.powermock', name: 'powermock-api-mockito2', version: '2.0.0'

`

When I run test like this, it can be run success.
`
@RunWith(AndroidJUnit4.class)
public class UtilTest {

@Test
public void testUtil(){
    String test = HomeCountryUtil.genCountry();
    assert test != null;
}

}
`

But when I replace RunWith by PowerMock，it run failed.
`
@RunWith(PowerMockRunner.class)
public class UtilTest {

@Test
public void testUtil(){
    String test = HomeCountryUtil.genCountry();
    assert test != null;
}

}
`

The exception log :
E/TestRunner: failed: initializationError(com.lyhexample.firstapp.mock.UtilTest) ----- begin exception ----- E/TestRunner: java.lang.NoClassDefFoundError: Failed resolution of: Ljava/beans/Introspector; at org.powermock.configuration.support.ConfigurationMapper.map(ConfigurationMapper.java:44) at org.powermock.configuration.support.ConfigurationBuilder$ConfigurationCreator.mapConfiguration(ConfigurationBuilder.java:80) at org.powermock.configuration.support.ConfigurationBuilder$ConfigurationCreator.create(ConfigurationBuilder.java:69) at org.powermock.configuration.support.ConfigurationBuilder.fromProperties(ConfigurationBuilder.java:54) at org.powermock.configuration.support.ConfigurationFactoryImpl.readEnvironmentConfiguration(ConfigurationFactoryImpl.java:62) at org.powermock.configuration.support.ConfigurationFactoryImpl.create(ConfigurationFactoryImpl.java:52) at org.powermock.configuration.GlobalConfiguration.createConfig(GlobalConfiguration.java:75) at org.powermock.configuration.GlobalConfiguration.<init>(GlobalConfiguration.java:59) at org.powermock.configuration.GlobalConfiguration.powerMockConfiguration(GlobalConfiguration.java:44) at org.powermock.core.classloader.ByteCodeFramework.getByteCodeFrameworkForTestClass(ByteCodeFramework.java:49) at org.powermock.core.transformers.TestClassTransformerBuilder.removesTestMethodAnnotation(TestClassTransformerBuilder.java:25) at org.powermock.tests.utils.impl.AbstractCommonTestSuiteChunkerImpl.createDefaultMockLoader(AbstractCommonTestSuiteChunkerImpl.java:125) at org.powermock.tests.utils.impl.AbstractCommonTestSuiteChunkerImpl.chunkClass(AbstractCommonTestSuiteChunkerImpl.java:89) at org.powermock.tests.utils.impl.AbstractCommonTestSuiteChunkerImpl.<init>(AbstractCommonTestSuiteChunkerImpl.java:50) at org.powermock.tests.utils.impl.AbstractCommonTestSuiteChunkerImpl.<init>(AbstractCommonTestSuiteChunkerImpl.java:44) at org.powermock.tests.utils.impl.AbstractTestSuiteChunkerImpl.<init>(AbstractTestSuiteChunkerImpl.java:57) at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.<init>(JUnit4TestSuiteChunkerImpl.java:57) at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.<init>(AbstractCommonPowerMockRunner.java:36) at org.powermock.modules.junit4.PowerMockRunner.<init>(PowerMockRunner.java:34) at java.lang.reflect.Constructor.newInstance0(Native Method) at java.lang.reflect.Constructor.newInstance(Constructor.java:343) at org.junit.internal.builders.AnnotatedBuilder.buildRunner(AnnotatedBuilder.java:104) at org.junit.internal.builders.AnnotatedBuilder.runnerForClass(AnnotatedBuilder.java:86) at androidx.test.internal.runner.junit4.AndroidAnnotatedBuilder.runnerForClass(AndroidAnnotatedBuilder.java:63) at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:59) at org.junit.internal.builders.AllDefaultPossibilitiesBuilder.runnerForClass(AllDefaultPossibilitiesBuilder.java:26) at androidx.test.internal.runner.AndroidRunnerBuilder.runnerForClass(AndroidRunnerBuilder.java:153) at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:59) at androidx.test.internal.runner.TestLoader.doCreateRunner(TestLoader.java:73) at androidx.test.internal.runner.TestLoader.getRunnersFor(TestLoader.java:104) at androidx.test.internal.runner.TestRequestBuilder.build(TestRequestBuilder.java:789) at androidx.test.runner.AndroidJUnitRunner.buildRequest(AndroidJUnitRunner.java:543) at androidx.test.runner.AndroidJUnitRunner.onStart(AndroidJUnitRunner.java:386) at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:2251) Caused by: java.lang.ClassNotFoundException: Didn't find class "java.beans.Introspector" on path: DexPathList[[zip file "/data/app/com.lyhexample.firstapp.test-78UV7bYZZe9yyKyM8szOOA==/base.apk", zip file "/data/app/com.lyhexample.firstapp-Mm7510nQw6GUeYxDzZ8MNA==/base.apk"],nativeLibraryDirectories=[/data/app/com.lyhexample.firstapp.test-78UV7bYZZe9yyKyM8szOOA==/lib/arm64, /data/app/com.lyhexample.firstapp-Mm7510nQw6GUeYxDzZ8MNA==/lib/arm64, /system/lib64, /system/product/lib64, /hw_product/lib64, /sys ----- end exception ----- I/TestRunner: finished: initializationError(com.lyhexample.firstapp.mock.UtilTest) I/xample.firstap: jit_compiled:[OK] java.lang.Object java.lang.ref.Reference.get() @ /apex/com.android.runtime/javalib/core-oj.jar I/MonitoringInstr: Activities that are still in CREATED to STOPPED: 0 I/TestRunner: run finished: 1 tests, 1 failed, 0 ignored