Local Unit Testing for DataStore

To do unit test for persistence layer (datastore), you need the following libraries in the classpath:

• ${SDK_ROOT}/lib/impl/appengine-api.jar
• ${SDK_ROOT}/lib/impl/appengine-api-labs.jar
• ${SDK_ROOT}/lib/impl/appengine-api-stubs.jar
• ${SDK_ROOT}/lib/testing/appengine-testing.jar

Once done, run the example below:

import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.Entity;
import static com.google.appengine.api.datastore.FetchOptions.Builder.withLimit;
import com.google.appengine.api.datastore.Query;
import com.google.appengine.tools.development.testing.LocalDatastoreServiceTestConfig;
import com.google.appengine.tools.development.testing.LocalServiceTestHelper;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import static org.junit.Assert.*;
public class LocalDatastoreTest {

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

    @Before
    public void setUp() {
        helper.setUp();
    }

    @After
    public void tearDown() {
        helper.tearDown();
    }

    // run this test twice to prove we're not leaking any state across tests
    private void doTest() {
        DatastoreService ds = DatastoreServiceFactory.getDatastoreService();
        assertEquals(0, ds.prepare(new Query("yam")).countEntities(withLimit(10)));
        ds.put(new Entity("yam"));
        ds.put(new Entity("yam"));
        assertEquals(2, ds.prepare(new Query("yam")).countEntities(withLimit(10)));
    }

    @Test
    public void testInsert1() {
        doTest();
    }

    @Test
    public void testInsert2() {
        doTest();
    }
}

For more details, you may read the source.

https://developers.google.com/appengine/docs/java/tools/localunittesting