Unit testing Cloud Datastore with Android Studio

I am trying to write unit tests for a Cloud Endpoints backend, specifically using Datastore. (Unit testing without access to any specific Android modules is working as expected.)

Per this question, I added the following to my backend's build.gradle:

testCompile 'com.google.appengine:appengine-api-labs:1.9.8'
testCompile 'com.google.appengine:appengine-api-stubs:1.9.8'
testCompile 'com.google.appengine:appengine-testing:1.9.8'
testCompile 'junit:junit:4.12+'

My code is minimized from this tutorial and located at backend/src/test/java/<package>:

import com.google.appengine.tools.development.testing.LocalDatastoreServiceTestConfig;
import com.google.appengine.tools.development.testing.LocalServiceTestHelper;

import org.junit.Test;

import static junit.framework.Assert.assertTrue;

public class ExampleDatastoreTest {

    private final LocalServiceTestHelper datastoreHelper =
            new LocalServiceTestHelper(new LocalDatastoreServiceTestConfig());

    @org.junit.Before
    public void setUp() throws Exception {
        datastoreHelper.setUp();
    }

    @org.junit.After
    public void tearDown() throws Exception {
        datastoreHelper.tearDown();
    }

    @Test
    public void testExample() {
        assertTrue(true);
    }
}

I am getting NoClassDefFoundError when I call tearDown on my LocalServiceTestHelper.

Per that tutorial, I still need to include:

${SDK_ROOT}/lib/impl/appengine-api.jar
${SDK_ROOT}/lib/impl/appengine-tools-sdk.jar

Using File > Project Structure in Android Studio 1.2.2, I found these options:

testCompile 'com.google.appengine:appengine-tools-sdk:1.9.25'
testCompile 'com.google.appengine:appengine-api-1.0-sdk:1.9.25'
testCompile 'com.google.appengine:appengine:1.9.25'

The appengine-tools-sdk looks good, but I don't seem to be able to find appengine-api. The two I listed above are the closest I found. I continue to get the same error.

What am I missing here?