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Testing - Java SDK

On this page

  • Integration Tests
  • Application Context
  • Looper Thread
  • Delay Test Execution While Async Calls Complete
  • Testing Backend
  • Testing Atlas Cluster
  • Full Example
  • Unit Tests
  • Full Example

You can test your application using unit tests or integration tests. Unit tests only assess the logic written in your application's code. Integration tests assess your application logic, database queries and writes, and calls to your application's backend, if you have one. Unit tests run on your development machine using the JVM, while integration tests run on a physical or emulated Android device. You can run integration tests by communicating with actual instances of Realm or an App backend using Android's built-in instrumented tests.

Android uses specific file paths and folder names in Android projects for unit tests and instrumented tests:

Test Type
Path
Unit Tests
/app/src/test
Instrumented Tests
/app/src/androidTest

Because the SDK uses C++ code via Android Native for data storage, unit testing requires you to entirely mock interactions with Realm. Prefer integration tests for logic that requires extensive interaction with the database.

Integration Tests

This section shows how to integration test an application that uses the Realm SDK. It covers the following concepts in the test environment:

  • acquiring an application context

  • executing logic on a Looper thread

  • how to delay test execution while asynchronous method calls complete

Applications that use Sync or a backend App also require (not covered here):

  • a separate App backend for testing, with separate user accounts and data

  • a separate Atlas cluster containing test-only data

Application Context

To initialize the SDK, you'll need to provide an application or activity context. This isn't available by default in Android integration tests. However, you can use Android's built-in testing ActivityScenario class to start an activity in your tests. You can use any activity from your application, or you can create an empty activity just for testing. Call ActivityScenario.launch() with your activity class as a parameter to start the simulated activity.

Next, use the ActivityScenario.onActivity() method to run a lambda on the simulated activity's main thread. In this lambda, you should call the Realm.init() function to initialize the SDK with your activity as a parameter. Additionally, you should save the parameter passed to your lambda (the newly created instance of your activity) for future use.

Because the onActivity() method runs on a different thread, you should block your test from executing further until this initial setup completes.

The following example uses an ActivityScenario, an empty testing activity, and a CountDownLatch to demonstrate how to set up an environment where you can test your Realm application:

AtomicReference<Activity> testActivity = new AtomicReference<Activity>();
ActivityScenario<BasicActivity> scenario = ActivityScenario.launch(BasicActivity.class);
// create a latch to force blocking for an async call to initialize realm
CountDownLatch setupLatch = new CountDownLatch(1);
scenario.onActivity(activity -> {
    Realm.init(activity);
    testActivity.set(activity);
    setupLatch.countDown(); // unblock the latch await
});
// block until we have an activity to run tests on
try {
    Assert.assertTrue(setupLatch.await(1, TimeUnit.SECONDS));
} catch (InterruptedException e) {
    Log.e("EXAMPLE", e.getMessage());
}
var testActivity: Activity? = null
val scenario: ActivityScenario<BasicActivity>? =
    ActivityScenario.launch(BasicActivity::class.java)
// create a latch to force blocking for an async call to initialize realm
val setupLatch = CountDownLatch(1)
scenario?.onActivity{ activity: BasicActivity ->
    Realm.init(activity)
    testActivity = activity
    setupLatch.countDown() // unblock the latch await
}

Looper Thread

Realm functionality such as Live objects and change notifications only work on Looper threads. Threads configured with a Looper object pass events over a message loop coordinated by the Looper. Test functions normally don't have a Looper object, and configuring one to work in your tests can be very error-prone.

Instead, you can use the Activity.runOnUiThread() method of your test activity to execute logic on a thread that already has a Looper configured. Combine Activity.runOnUiThread() with a CountDownLatch as described in the delay section to prevent your test from completing and exiting before your logic has executed. Within the runOnUiThread() call, you can interact with the SDK just like you normally would in your application code:

testActivity.get().runOnUiThread(() -> {
    // instantiate an app connection
    String appID = YOUR_APP_ID; // replace this with your test application App ID
    App app = new App(new AppConfiguration.Builder(appID).build());
    // authenticate a user
    Credentials credentials = Credentials.anonymous();
    app.loginAsync(credentials, it -> {
        if (it.isSuccess()) {
            Log.v("EXAMPLE", "Successfully authenticated.");
            // open a synced realm
            SyncConfiguration config = new SyncConfiguration.Builder(
                    app.currentUser(),
                    getRandomPartition()) // replace this with a valid partition
                    .allowQueriesOnUiThread(true)
                    .allowWritesOnUiThread(true)
                    .build();
            Realm.getInstanceAsync(config, new Realm.Callback() {
                @Override
                public void onSuccess(@NonNull Realm realm) {
                    Log.v("EXAMPLE", "Successfully opened a realm.");
                    // read and write to realm here via transactions
                    testLatch.countDown();
                    realm.executeTransaction(new Realm.Transaction() {
                        @Override
                        public void execute(@NonNull Realm realm) {
                            realm.createObjectFromJson(Frog.class,
                                    "{ name: \"Doctor Cucumber\", age: 1, species: \"bullfrog\", owner: \"Wirt\", _id: 0 }");
                        }
                    });
                    realm.close();
                }
                @Override
                public void onError(@NonNull Throwable exception) {
                    Log.e("EXAMPLE", "Failed to open the realm: " + exception.getLocalizedMessage());
                }
            });
        } else {
            Log.e("EXAMPLE", "Failed login: " + it.getError().getErrorMessage());
        }
    });
});
testActivity?.runOnUiThread {
    // instantiate an app connection
    val appID: String = YOUR_APP_ID // replace this with your App ID
    val app = App(AppConfiguration.Builder(appID).build())
    // authenticate a user
    val credentials = Credentials.anonymous()
    app.loginAsync(credentials) {
        if (it.isSuccess) {
            Log.v("EXAMPLE", "Successfully authenticated.")
            // open a synced realm
            val config = SyncConfiguration.Builder(
                app.currentUser(),
                getRandomPartition() // replace this with a valid partition
            ).allowQueriesOnUiThread(true)
                .allowWritesOnUiThread(true)
                .build()
            Realm.getInstanceAsync(config, object : Realm.Callback() {
                override fun onSuccess(realm: Realm) {
                    Log.v("EXAMPLE", "Successfully opened a realm.")
                    // read and write to realm here via transactions
                    realm.executeTransaction {
                        realm.createObjectFromJson(
                            Frog::class.java,
                            "{ name: \"Doctor Cucumber\", age: 1, species: \"bullfrog\", owner: \"Wirt\", _id:0 }"
                        )
                    }
                    testLatch.countDown()
                    realm.close()
                }
                override fun onError(exception: Throwable) {
                    Log.e("EXAMPLE",
                        "Failed to open the realm: " + exception.localizedMessage)
                }
            })
        } else {
            Log.e("EXAMPLE", "Failed login: " + it.error.errorMessage)
        }
    }
}

Delay Test Execution While Async Calls Complete

Because the SDK uses asynchronous calls for common operations such as database queries, authentication, and function calls, tests need a way to wait for those async calls to complete. Otherwise, your tests will exit before your asynchronous (or multi-threaded) calls run. This example uses Java's built-in CountDownLatch. Follow these steps to use a CountDownLatch in your own tests:

  1. Instantiate a CountDownLatch with a count of 1.

  2. After running the async logic your test needs to wait for, call that CountDownLatch instance's countDown() method.

  3. When you need to wait for async logic, add a try/catch block that handles an InterruptedException. In that block, call that CountDownLatch instance's await() method.

  4. Pass a timeout interval and unit to await(), and wrap the call in a Assert.assertTrue() assertion. If the logic takes too long, the await() call times out, returning false and failing the test.

The following example demonstrates the use of a CountDownLatch to wait for authentication and opening a realm asynchronously on a separate thread:

CountDownLatch testLatch = new CountDownLatch(1);
testActivity.get().runOnUiThread(() -> {
    // instantiate an app connection
    String appID = YOUR_APP_ID; // replace this with your test application App ID
    App app = new App(new AppConfiguration.Builder(appID).build());
    // authenticate a user
    Credentials credentials = Credentials.anonymous();
    app.loginAsync(credentials, it -> {
        if (it.isSuccess()) {
            Log.v("EXAMPLE", "Successfully authenticated.");
            // open a synced realm
            SyncConfiguration config = new SyncConfiguration.Builder(
                    app.currentUser(),
                    getRandomPartition()) // replace this with a valid partition
                    .allowQueriesOnUiThread(true)
                    .allowWritesOnUiThread(true)
                    .build();
            Realm.getInstanceAsync(config, new Realm.Callback() {
                @Override
                public void onSuccess(@NonNull Realm realm) {
                    Log.v("EXAMPLE", "Successfully opened a realm.");
                    // read and write to realm here via transactions
                    testLatch.countDown();
                    realm.executeTransaction(new Realm.Transaction() {
                        @Override
                        public void execute(@NonNull Realm realm) {
                            realm.createObjectFromJson(Frog.class,
                                    "{ name: \"Doctor Cucumber\", age: 1, species: \"bullfrog\", owner: \"Wirt\", _id: 0 }");
                        }
                    });
                    realm.close();
                }
                @Override
                public void onError(@NonNull Throwable exception) {
                    Log.e("EXAMPLE", "Failed to open the realm: " + exception.getLocalizedMessage());
                }
            });
        } else {
            Log.e("EXAMPLE", "Failed login: " + it.getError().getErrorMessage());
        }
    });
});
// block until the async calls in the test succeed or error out
try {
    Assert.assertTrue(testLatch.await(5, TimeUnit.SECONDS));
} catch (InterruptedException e) {
    Log.e("EXAMPLE", e.getMessage());
}
val testLatch = CountDownLatch(1)
testActivity?.runOnUiThread {
    // instantiate an app connection
    val appID: String = YOUR_APP_ID // replace this with your App ID
    val app = App(AppConfiguration.Builder(appID).build())
    // authenticate a user
    val credentials = Credentials.anonymous()
    app.loginAsync(credentials) {
        if (it.isSuccess) {
            Log.v("EXAMPLE", "Successfully authenticated.")
            // open a synced realm
            val config = SyncConfiguration.Builder(
                app.currentUser(),
                getRandomPartition() // replace this with a valid partition
            ).allowQueriesOnUiThread(true)
                .allowWritesOnUiThread(true)
                .build()
            Realm.getInstanceAsync(config, object : Realm.Callback() {
                override fun onSuccess(realm: Realm) {
                    Log.v("EXAMPLE", "Successfully opened a realm.")
                    // read and write to realm here via transactions
                    realm.executeTransaction {
                        realm.createObjectFromJson(
                            Frog::class.java,
                            "{ name: \"Doctor Cucumber\", age: 1, species: \"bullfrog\", owner: \"Wirt\", _id:0 }"
                        )
                    }
                    testLatch.countDown()
                    realm.close()
                }
                override fun onError(exception: Throwable) {
                    Log.e("EXAMPLE",
                        "Failed to open the realm: " + exception.localizedMessage)
                }
            })
        } else {
            Log.e("EXAMPLE", "Failed login: " + it.error.errorMessage)
        }
    }
}
// block until the async calls in the test succeed or error out
try {
    Assert.assertTrue(testLatch.await(5, TimeUnit.SECONDS))
} catch (e: InterruptedException) {
    Log.e("EXAMPLE", e.stackTraceToString())
}

Testing Backend

Applications that use an App backend should not connect to the production backend for testing purposes for the following reasons:

  • you should always keep test users and production users separate for security and privacy reasons

  • tests often require a clean initial state, so there's a good chance your tests will include a setup or teardown method that deletes all users or large chunks of data

You can use environments to manage separate apps for testing and production.

Testing Atlas Cluster

Applications that use Sync or MongoDB queries may read, write, update, or delete data stored in connected Atlas clusters. For security purposes, you shouldn't store production data and testing data on the same cluster. Additionally, tests may require schema changes before those changes are gracefully handled in your production application. As a result, you should use a separate Atlas cluster when testing your application.

Full Example

The following example shows a full Junit instrumented androidTest example running Realm in integration tests:

package com.mongodb.realm.examples.java;
import android.app.Activity;
import android.util.Log;
import androidx.annotation.NonNull;
import androidx.test.core.app.ActivityScenario;
import com.mongodb.realm.examples.BasicActivity;
import com.mongodb.realm.examples.model.kotlin.Frog;
import org.junit.Assert;
import org.junit.Test;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import io.realm.Realm;
import io.realm.mongodb.App;
import io.realm.mongodb.AppConfiguration;
import io.realm.mongodb.Credentials;
import io.realm.mongodb.sync.SyncConfiguration;
import static com.mongodb.realm.examples.RealmTestKt.YOUR_APP_ID;
import static com.mongodb.realm.examples.RealmTestKt.getRandomPartition;
public class TestTest {
    @Test
    public void testTesting() {
        AtomicReference<Activity> testActivity = new AtomicReference<Activity>();
        ActivityScenario<BasicActivity> scenario = ActivityScenario.launch(BasicActivity.class);
        // create a latch to force blocking for an async call to initialize realm
        CountDownLatch setupLatch = new CountDownLatch(1);
        scenario.onActivity(activity -> {
            Realm.init(activity);
            testActivity.set(activity);
            setupLatch.countDown(); // unblock the latch await
        });
        // block until we have an activity to run tests on
        try {
            Assert.assertTrue(setupLatch.await(1, TimeUnit.SECONDS));
        } catch (InterruptedException e) {
            Log.e("EXAMPLE", e.getMessage());
        }
        CountDownLatch testLatch = new CountDownLatch(1);
        testActivity.get().runOnUiThread(() -> {
            // instantiate an app connection
            String appID = YOUR_APP_ID; // replace this with your test application App ID
            App app = new App(new AppConfiguration.Builder(appID).build());
            // authenticate a user
            Credentials credentials = Credentials.anonymous();
            app.loginAsync(credentials, it -> {
                if (it.isSuccess()) {
                    Log.v("EXAMPLE", "Successfully authenticated.");
                    // open a synced realm
                    SyncConfiguration config = new SyncConfiguration.Builder(
                            app.currentUser(),
                            getRandomPartition()) // replace this with a valid partition
                            .allowQueriesOnUiThread(true)
                            .allowWritesOnUiThread(true)
                            .build();
                    Realm.getInstanceAsync(config, new Realm.Callback() {
                        @Override
                        public void onSuccess(@NonNull Realm realm) {
                            Log.v("EXAMPLE", "Successfully opened a realm.");
                            // read and write to realm here via transactions
                            testLatch.countDown();
                            realm.executeTransaction(new Realm.Transaction() {
                                @Override
                                public void execute(@NonNull Realm realm) {
                                    realm.createObjectFromJson(Frog.class,
                                            "{ name: \"Doctor Cucumber\", age: 1, species: \"bullfrog\", owner: \"Wirt\", _id: 0 }");
                                }
                            });
                            realm.close();
                        }
                        @Override
                        public void onError(@NonNull Throwable exception) {
                            Log.e("EXAMPLE", "Failed to open the realm: " + exception.getLocalizedMessage());
                        }
                    });
                } else {
                    Log.e("EXAMPLE", "Failed login: " + it.getError().getErrorMessage());
                }
            });
        });
        // block until the async calls in the test succeed or error out
        try {
            Assert.assertTrue(testLatch.await(5, TimeUnit.SECONDS));
        } catch (InterruptedException e) {
            Log.e("EXAMPLE", e.getMessage());
        }
    }
}
package com.mongodb.realm.examples.kotlin
import android.app.Activity
import android.util.Log
import androidx.test.core.app.ActivityScenario
import com.mongodb.realm.examples.BasicActivity
import com.mongodb.realm.examples.YOUR_APP_ID
import com.mongodb.realm.examples.getRandomPartition
import com.mongodb.realm.examples.model.kotlin.Frog
import io.realm.Realm
import io.realm.mongodb.App
import io.realm.mongodb.AppConfiguration
import io.realm.mongodb.Credentials
import io.realm.mongodb.sync.SyncConfiguration
import java.util.concurrent.CountDownLatch
import java.util.concurrent.TimeUnit
import org.junit.Assert
import org.junit.Test
class TestTest {
    @Test
    fun testTesting() {
        var testActivity: Activity? = null
        val scenario: ActivityScenario<BasicActivity>? =
            ActivityScenario.launch(BasicActivity::class.java)
        // create a latch to force blocking for an async call to initialize realm
        val setupLatch = CountDownLatch(1)
        scenario?.onActivity{ activity: BasicActivity ->
            Realm.init(activity)
            testActivity = activity
            setupLatch.countDown() // unblock the latch await
        }
        // block until we have an activity to run tests on
        try {
            Assert.assertTrue(setupLatch.await(1, TimeUnit.SECONDS))
        } catch (e: InterruptedException) {
            Log.e("EXAMPLE", e.stackTraceToString())
        }
        val testLatch = CountDownLatch(1)
        testActivity?.runOnUiThread {
            // instantiate an app connection
            val appID: String = YOUR_APP_ID // replace this with your App ID
            val app = App(AppConfiguration.Builder(appID).build())
            // authenticate a user
            val credentials = Credentials.anonymous()
            app.loginAsync(credentials) {
                if (it.isSuccess) {
                    Log.v("EXAMPLE", "Successfully authenticated.")
                    // open a synced realm
                    val config = SyncConfiguration.Builder(
                        app.currentUser(),
                        getRandomPartition() // replace this with a valid partition
                    ).allowQueriesOnUiThread(true)
                        .allowWritesOnUiThread(true)
                        .build()
                    Realm.getInstanceAsync(config, object : Realm.Callback() {
                        override fun onSuccess(realm: Realm) {
                            Log.v("EXAMPLE", "Successfully opened a realm.")
                            // read and write to realm here via transactions
                            realm.executeTransaction {
                                realm.createObjectFromJson(
                                    Frog::class.java,
                                    "{ name: \"Doctor Cucumber\", age: 1, species: \"bullfrog\", owner: \"Wirt\", _id:0 }"
                                )
                            }
                            testLatch.countDown()
                            realm.close()
                        }
                        override fun onError(exception: Throwable) {
                            Log.e("EXAMPLE",
                                "Failed to open the realm: " + exception.localizedMessage)
                        }
                    })
                } else {
                    Log.e("EXAMPLE", "Failed login: " + it.error.errorMessage)
                }
            }
        }
        // block until the async calls in the test succeed or error out
        try {
            Assert.assertTrue(testLatch.await(5, TimeUnit.SECONDS))
        } catch (e: InterruptedException) {
            Log.e("EXAMPLE", e.stackTraceToString())
        }
    }
}

Tip

See also:

See the Realm Documentation Examples App for an example of integration testing the SDK locally and with a live backend.

Unit Tests

To unit test Realm applications that use Realm, you must mock Realm (and your application backend, if you use one). Use the following libraries to mock SDK functionality:

To make these libraries available for unit testing in your Android project, add the following to the dependencies block of your application build.gradle file:

 testImplementation "org.robolectric:robolectric:4.1"
 testImplementation "org.mockito:mockito-core:3.3.3"
 testImplementation "org.powermock:powermock-module-junit4:2.0.9"
 testImplementation "org.powermock:powermock-module-junit4-rule:2.0.9"
 testImplementation "org.powermock:powermock-api-mockito2:2.0.9"
 testImplementation "org.powermock:powermock-classloading-xstream:2.0.9"

Note

Version Compatibility

Mocking the SDK in unit tests requires Robolectric, Mockito, and Powermock because the SDK uses Android Native C++ method calls to interact with Realm. Because the frameworks required to override these method calls can be delicate, you should use the versions listed above to ensure that your mocking is successful. Some recent version updates (particularly Robolectric version 4.2+) can break compiliation of unit tests using the SDK.

To configure your unit tests to use Robolectric, PowerMock, and Mockito with the SDK, add the following annotations to each unit test class that mocks the SDK:

@RunWith(RobolectricTestRunner.class)
@Config(sdk = 28)
@PowerMockIgnore({"org.mockito.*", "org.robolectric.*", "android.*", "jdk.internal.reflect.*", "androidx.*"})
@SuppressStaticInitializationFor("io.realm.internal.Util")
@PrepareForTest({Realm.class, RealmConfiguration.class, RealmQuery.class, RealmResults.class, RealmCore.class, RealmLog.class})
@RunWith(RobolectricTestRunner::class)
@Config(sdk = [28])
@PowerMockIgnore(
    "org.mockito.*",
    "org.robolectric.*",
    "android.*",
    "jdk.internal.reflect.*",
    "androidx.*"
)
@SuppressStaticInitializationFor("io.realm.internal.Util")
@PrepareForTest(
    Realm::class,
    RealmConfiguration::class,
    RealmQuery::class,
    RealmResults::class,
    RealmCore::class,
    RealmLog::class
)

Then, bootstrap Powermock globally in the test class:

// bootstrap powermock
@Rule
public PowerMockRule rule = new PowerMockRule();
// bootstrap powermock
@Rule
var rule = PowerMockRule()

Next, mock the components of the SDK that might query native C++ code so we don't hit the limitations of the test environment:

// set up realm SDK components to be mocked. The order of these matters
mockStatic(RealmCore.class);
mockStatic(RealmLog.class);
mockStatic(Realm.class);
mockStatic(RealmConfiguration.class);
Realm.init(RuntimeEnvironment.application);
// boilerplate to mock realm components -- this prevents us from hitting any
// native code
doNothing().when(RealmCore.class);
RealmCore.loadLibrary(any(Context.class));
// set up realm SDK components to be mocked. The order of these matters
PowerMockito.mockStatic(RealmCore::class.java)
PowerMockito.mockStatic(RealmLog::class.java)
PowerMockito.mockStatic(Realm::class.java)
PowerMockito.mockStatic(RealmConfiguration::class.java)
Realm.init(RuntimeEnvironment.application)
PowerMockito.doNothing().`when`(RealmCore::class.java)
RealmCore.loadLibrary(ArgumentMatchers.any(Context::class.java))

Once you've completed the setup required for mocking, you can start mocking components and wiring up behavior for your tests. You can also configure PowerMockito to return specific objects when new objects of a type are instantiated, so even code that references the default realm in your application won't break your tests:

// create the mocked realm
final Realm mockRealm = mock(Realm.class);
final RealmConfiguration mockRealmConfig = mock(RealmConfiguration.class);
// use this mock realm config for all new realm configurations
whenNew(RealmConfiguration.class).withAnyArguments().thenReturn(mockRealmConfig);
// use this mock realm for all new default realms
when(Realm.getDefaultInstance()).thenReturn(mockRealm);
// create the mocked realm
val mockRealm = PowerMockito.mock(Realm::class.java)
val mockRealmConfig = PowerMockito.mock(
    RealmConfiguration::class.java
)
// use this mock realm config for all new realm configurations
PowerMockito.whenNew(RealmConfiguration::class.java).withAnyArguments()
    .thenReturn(mockRealmConfig)
// use this mock realm for all new default realms
PowerMockito.`when`(Realm.getDefaultInstance()).thenReturn(mockRealm)

After mocking a realm, you'll have to configure data for your test cases. See the full example below for some examples of how you can provide testing data in unit tests.

Full Example

The following example shows a full JUnit test example mocking Realm in unit tests. This example tests an activity that performs some basic Realm operations. The tests use mocking to simulate those operations when that activity is started during a unit test:

package com.mongodb.realm.examples.java;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.os.AsyncTask;
import android.util.Log;
import android.widget.LinearLayout;
import android.widget.TextView;
import com.mongodb.realm.examples.R;
import com.mongodb.realm.examples.model.java.Cat;
import io.realm.Realm;
import io.realm.RealmResults;
public class UnitTestActivity extends AppCompatActivity {
    public static final String TAG = UnitTestActivity.class.getName();
    private LinearLayout rootLayout = null;
    private Realm realm;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Realm.init(getApplicationContext());
        setContentView(R.layout.activity_unit_test);
        rootLayout = findViewById(R.id.container);
        rootLayout.removeAllViews();
        // open the default Realm for the UI thread.
        realm = Realm.getDefaultInstance();
        // clean up from previous run
        cleanUp();
        // small operation that is ok to run on the main thread
        basicCRUD(realm);
        // more complex operations can be executed on another thread.
        AsyncTask<Void, Void, String> foo = new AsyncTask<Void, Void, String>() {
            @Override
            protected String doInBackground(Void... voids) {
                String info = "";
                info += complexQuery();
                return info;
            }
            @Override
            protected void onPostExecute(String result) {
                showStatus(result);
            }
        };
        foo.execute();
        findViewById(R.id.clean_up).setOnClickListener(view -> {
            view.setEnabled(false);
            Log.d("TAG", "clean up");
            cleanUp();
            view.setEnabled(true);
        });
    }
    private void cleanUp() {
        // delete all cats
        realm.executeTransaction(r -> r.delete(Cat.class));
    }
    @Override
    public void onDestroy() {
        super.onDestroy();
        realm.close(); // remember to close realm when done.
    }
    private void showStatus(String txt) {
        Log.i(TAG, txt);
        TextView tv = new TextView(this);
        tv.setText(txt);
        rootLayout.addView(tv);
    }
    private void basicCRUD(Realm realm) {
        showStatus("Perform basic Create/Read/Update/Delete (CRUD) operations...");
        // all writes must be wrapped in a transaction to facilitate safe multi threading
        realm.executeTransaction(r -> {
            // add a cat
            Cat cat = r.createObject(Cat.class);
            cat.setName("John Young");
        });
        // find the first cat (no query conditions) and read a field
        final Cat cat = realm.where(Cat.class).findFirst();
        showStatus(cat.getName());
        // update cat in a transaction
        realm.executeTransaction(r -> {
            cat.setName("John Senior");
        });
        showStatus(cat.getName());
        // add two more cats
        realm.executeTransaction(r -> {
            Cat jane = r.createObject(Cat.class);
            jane.setName("Jane");
            Cat doug = r.createObject(Cat.class);
            doug.setName("Robert");
        });
        RealmResults<Cat> cats = realm.where(Cat.class).findAll();
        showStatus(String.format("Found %s cats", cats.size()));
        for (Cat p : cats) {
            showStatus("Found " + p.getName());
        }
    }
    private String complexQuery() {
        String status = "\n\nPerforming complex Query operation...";
        Realm realm = Realm.getDefaultInstance();
        status += "\nNumber of cats in the DB: " + realm.where(Cat.class).count();
        // find all cats where name begins with "J".
        RealmResults<Cat> results = realm.where(Cat.class)
                .beginsWith("name", "J")
                .findAll();
        status += "\nNumber of cats whose name begins with 'J': " + results.size();
        realm.close();
        return status;
    }
}
import android.content.Context;
import com.mongodb.realm.examples.java.UnitTestActivity;
import com.mongodb.realm.examples.model.java.Cat;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.core.classloader.annotations.PowerMockIgnore;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.core.classloader.annotations.SuppressStaticInitializationFor;
import org.powermock.modules.junit4.rule.PowerMockRule;
import org.robolectric.Robolectric;
import org.robolectric.RobolectricTestRunner;
import org.robolectric.RuntimeEnvironment;
import org.robolectric.annotation.Config;
import java.util.Arrays;
import java.util.List;
import io.realm.Realm;
import io.realm.RealmConfiguration;
import io.realm.RealmObject;
import io.realm.RealmQuery;
import io.realm.RealmResults;
import io.realm.internal.RealmCore;
import io.realm.log.RealmLog;
import com.mongodb.realm.examples.R;
import static org.mockito.Matchers.any;
import static org.mockito.Matchers.anyInt;
import static org.mockito.Matchers.anyString;
import static org.mockito.Mockito.doCallRealMethod;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import static org.powermock.api.mockito.PowerMockito.doNothing;
import static org.powermock.api.mockito.PowerMockito.mock;
import static org.powermock.api.mockito.PowerMockito.mockStatic;
import static org.powermock.api.mockito.PowerMockito.when;
import static org.powermock.api.mockito.PowerMockito.whenNew;
@RunWith(RobolectricTestRunner.class)
@Config(sdk = 28)
@PowerMockIgnore({"org.mockito.*", "org.robolectric.*", "android.*", "jdk.internal.reflect.*", "androidx.*"})
@SuppressStaticInitializationFor("io.realm.internal.Util")
@PrepareForTest({Realm.class, RealmConfiguration.class, RealmQuery.class, RealmResults.class, RealmCore.class, RealmLog.class})
public class TestTest {
    // bootstrap powermock
    @Rule
    public PowerMockRule rule = new PowerMockRule();
    // mocked realm SDK components for tests
    private Realm mockRealm;
    private RealmResults<Cat> cats;
    @Before
    public void setup() throws Exception {
        // set up realm SDK components to be mocked. The order of these matters
        mockStatic(RealmCore.class);
        mockStatic(RealmLog.class);
        mockStatic(Realm.class);
        mockStatic(RealmConfiguration.class);
        Realm.init(RuntimeEnvironment.application);
        // boilerplate to mock realm components -- this prevents us from hitting any
        // native code
        doNothing().when(RealmCore.class);
        RealmCore.loadLibrary(any(Context.class));
        // create the mocked realm
        final Realm mockRealm = mock(Realm.class);
        final RealmConfiguration mockRealmConfig = mock(RealmConfiguration.class);
        // use this mock realm config for all new realm configurations
        whenNew(RealmConfiguration.class).withAnyArguments().thenReturn(mockRealmConfig);
        // use this mock realm for all new default realms
        when(Realm.getDefaultInstance()).thenReturn(mockRealm);
        // any time we ask Realm to create a Cat, return a new instance.
        when(mockRealm.createObject(Cat.class)).thenReturn(new Cat());
        // set up test data
        Cat p1 = new Cat();
        p1.setName("Enoch");
        Cat p2 = new Cat();
        p2.setName("Quincy Endicott");
        Cat p3 = new Cat();
        p3.setName("Sara");
        Cat p4 = new Cat();
        p4.setName("Jimmy Brown");
        List<Cat> catList = Arrays.asList(p1, p2, p3, p4);
        // create a mocked RealmQuery
        RealmQuery<Cat> catQuery = mockRealmQuery();
        // when the RealmQuery performs findFirst, return the first record in the list.
        when(catQuery.findFirst()).thenReturn(catList.get(0));
        // when the where clause is called on the Realm, return the mock query.
        when(mockRealm.where(Cat.class)).thenReturn(catQuery);
        // when the RealmQuery is filtered on any string and any integer, return the query
        when(catQuery.equalTo(anyString(), anyInt())).thenReturn(catQuery);
        // when a between query is performed with any string as the field and any int as the
        // value, then return the catQuery itself
        when(catQuery.between(anyString(), anyInt(), anyInt())).thenReturn(catQuery);
        // When a beginsWith clause is performed with any string field and any string value
        // return the same cat query
        when(catQuery.beginsWith(anyString(), anyString())).thenReturn(catQuery);
        // RealmResults is final, must mock static and also place this in the PrepareForTest
        // annotation array.
        mockStatic(RealmResults.class);
        // create a mock RealmResults
        RealmResults<Cat> cats = mockRealmResults();
        // the for(...) loop in Java needs an iterator, so we're giving it one that has items,
        // since the mock RealmResults does not provide an implementation. Therefore, any time
        // anyone asks for the RealmResults Iterator, give them a functioning iterator from the
        // ArrayList of Cats we created above. This will allow the loop to execute.
        when(cats.iterator()).thenReturn(catList.iterator());
        // Return the size of the mock list.
        when(cats.size()).thenReturn(catList.size());
        // when we ask Realm for all of the Cat instances, return the mock RealmResults
        when(mockRealm.where(Cat.class).findAll()).thenReturn(cats);
        // when we ask the RealmQuery for all of the Cat objects, return the mock RealmResults
        when(catQuery.findAll()).thenReturn(cats);
        this.mockRealm = mockRealm;
        this.cats = cats;
    }
    @Test
    public void shouldBeAbleToAccessActivityAndVerifyRealmInteractions() {
        doCallRealMethod().when(mockRealm)
                .executeTransaction(any(Realm.Transaction.class));
        // create test activity --  onCreate method calls methods that
        // query/write to realm
        UnitTestActivity activity = Robolectric
                .buildActivity(UnitTestActivity.class)
                .create()
                .start()
                .resume()
                .visible()
                .get();
        // click the clean up button
        activity.findViewById(R.id.clean_up).performClick();
        // verify that we queried for Cat instances five times in this run
        // (2 in basicCrud(), 2 in complexQuery() and 1 in the button click)
        verify(mockRealm, times(5)).where(Cat.class);
        // verify that the delete method was called. We also call delete at
        // the start of the activity to ensure we start with a clean db.
        verify(mockRealm, times(2)).delete(Cat.class);
        // call the destroy method so we can verify that the .close() method
        // was called (below)
        activity.onDestroy();
        // verify that the realm got closed 2 separate times. Once in the
        // AsyncTask, once in onDestroy
        verify(mockRealm, times(2)).close();
    }
    @SuppressWarnings("unchecked")
    private <T extends RealmObject> RealmQuery<T> mockRealmQuery() {
        return mock(RealmQuery.class);
    }
    @SuppressWarnings("unchecked")
    private <T extends RealmObject> RealmResults<T> mockRealmResults() {
        return mock(RealmResults.class);
    }
}
package com.mongodb.realm.examples.kotlin
import android.os.AsyncTask
import android.os.Bundle
import android.util.Log
import android.view.View
import android.widget.LinearLayout
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import com.mongodb.realm.examples.R
import com.mongodb.realm.examples.model.java.Cat
import io.realm.Realm
class UnitTestActivity : AppCompatActivity() {
    private var rootLayout: LinearLayout? = null
    private var realm: Realm? = null
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        Realm.init(applicationContext)
        setContentView(R.layout.activity_unit_test)
        rootLayout = findViewById(R.id.container)
        rootLayout!!.removeAllViews()
        // open the default Realm for the UI thread.
        realm = Realm.getDefaultInstance()
        // clean up from previous run
        cleanUp()
        // small operation that is ok to run on the main thread
        basicCRUD(realm)
        // more complex operations can be executed on another thread.
        val foo: AsyncTask<Void?, Void?, String> = object : AsyncTask<Void?, Void?, String>() {
            protected override fun doInBackground(vararg params: Void?): String? {
                var info = ""
                info += complexQuery()
                return info
            }
            override fun onPostExecute(result: String) {
                showStatus(result)
            }
        }
        foo.execute()
        findViewById<View>(R.id.clean_up).setOnClickListener { view: View ->
            view.isEnabled = false
            Log.d("TAG", "clean up")
            cleanUp()
            view.isEnabled = true
        }
    }
    private fun cleanUp() {
        // delete all cats
        realm!!.executeTransaction { r: Realm -> r.delete(Cat::class.java) }
    }
    public override fun onDestroy() {
        super.onDestroy()
        realm!!.close() // remember to close realm when done.
    }
    private fun showStatus(txt: String) {
        Log.i(TAG, txt)
        val tv = TextView(this)
        tv.text = txt
        rootLayout!!.addView(tv)
    }
    private fun basicCRUD(realm: Realm?) {
        showStatus("Perform basic Create/Read/Update/Delete (CRUD) operations...")
        // all writes must be wrapped in a transaction to facilitate safe multi threading
        realm!!.executeTransaction { r: Realm ->
            // add a cat
            val cat = r.createObject(Cat::class.java)
            cat.name = "John Young"
        }
        // find the first cat (no query conditions) and read a field
        val cat = realm.where(Cat::class.java).findFirst()
        showStatus(cat!!.name)
        // update cat in a transaction
        realm.executeTransaction { r: Realm? ->
            cat.name = "John Senior"
        }
        showStatus(cat.name)
        // add two more cats
        realm.executeTransaction { r: Realm ->
            val jane = r.createObject(Cat::class.java)
            jane.name = "Jane"
            val doug = r.createObject(Cat::class.java)
            doug.name = "Robert"
        }
        val cats = realm.where(Cat::class.java).findAll()
        showStatus(String.format("Found %s cats", cats.size))
        for (p in cats) {
            showStatus("Found " + p.name)
        }
    }
    private fun complexQuery(): String {
        var status = "\n\nPerforming complex Query operation..."
        val realm = Realm.getDefaultInstance()
        status += """
            
            Number of cats in the DB: ${realm.where(Cat::class.java).count()}
            """.trimIndent()
        // find all cats where name begins with "J".
        val results = realm.where(Cat::class.java)
            .beginsWith("name", "J")
            .findAll()
        status += """
            
            Number of cats whose name begins with 'J': ${results.size}
            """.trimIndent()
        realm.close()
        return status
    }
    companion object {
        val TAG = UnitTestActivity::class.java.name
    }
}
import android.content.Context
import android.view.View
import com.mongodb.realm.examples.R
import com.mongodb.realm.examples.kotlin.UnitTestActivity
import com.mongodb.realm.examples.model.java.Cat
import io.realm.Realm
import io.realm.RealmConfiguration
import io.realm.RealmObject
import io.realm.RealmQuery
import io.realm.RealmResults
import io.realm.internal.RealmCore
import io.realm.log.RealmLog
import java.lang.Exception
import java.util.*
import org.junit.Before
import org.junit.Rule
import org.junit.Test
import org.junit.runner.RunWith
import org.mockito.ArgumentMatchers
import org.mockito.Mockito
import org.powermock.api.mockito.PowerMockito
import org.powermock.core.classloader.annotations.PowerMockIgnore
import org.powermock.core.classloader.annotations.PrepareForTest
import org.powermock.core.classloader.annotations.SuppressStaticInitializationFor
import org.powermock.modules.junit4.rule.PowerMockRule
import org.robolectric.Robolectric
import org.robolectric.RobolectricTestRunner
import org.robolectric.RuntimeEnvironment
import org.robolectric.annotation.Config
@RunWith(RobolectricTestRunner::class)
@Config(sdk = [28])
@PowerMockIgnore(
    "org.mockito.*",
    "org.robolectric.*",
    "android.*",
    "jdk.internal.reflect.*",
    "androidx.*"
)
@SuppressStaticInitializationFor("io.realm.internal.Util")
@PrepareForTest(
    Realm::class,
    RealmConfiguration::class,
    RealmQuery::class,
    RealmResults::class,
    RealmCore::class,
    RealmLog::class
)
class TestTest {
    // bootstrap powermock
    @Rule
    var rule = PowerMockRule()
    // mocked realm SDK components for tests
    private var mockRealm: Realm? = null
    private var cats: RealmResults<Cat>? = null
    @Before
    @Throws(Exception::class)
    fun setup() {
        // set up realm SDK components to be mocked. The order of these matters
        PowerMockito.mockStatic(RealmCore::class.java)
        PowerMockito.mockStatic(RealmLog::class.java)
        PowerMockito.mockStatic(Realm::class.java)
        PowerMockito.mockStatic(RealmConfiguration::class.java)
        Realm.init(RuntimeEnvironment.application)
        PowerMockito.doNothing().`when`(RealmCore::class.java)
        RealmCore.loadLibrary(ArgumentMatchers.any(Context::class.java))
        // create the mocked realm
        val mockRealm = PowerMockito.mock(Realm::class.java)
        val mockRealmConfig = PowerMockito.mock(
            RealmConfiguration::class.java
        )
        // use this mock realm config for all new realm configurations
        PowerMockito.whenNew(RealmConfiguration::class.java).withAnyArguments()
            .thenReturn(mockRealmConfig)
        // use this mock realm for all new default realms
        PowerMockito.`when`(Realm.getDefaultInstance()).thenReturn(mockRealm)
        // any time we ask Realm to create a Cat, return a new instance.
        PowerMockito.`when`(mockRealm.createObject(Cat::class.java)).thenReturn(Cat())
        // set up test data
        val p1 = Cat()
        p1.name = "Enoch"
        val p2 = Cat()
        p2.name = "Quincy Endicott"
        val p3 = Cat()
        p3.name = "Sara"
        val p4 = Cat()
        p4.name = "Jimmy Brown"
        val catList = Arrays.asList(p1, p2, p3, p4)
        // create a mocked RealmQuery
        val catQuery = mockRealmQuery<Cat>()
        // when the RealmQuery performs findFirst, return the first record in the list.
        PowerMockito.`when`(catQuery!!.findFirst()).thenReturn(catList[0])
        // when the where clause is called on the Realm, return the mock query.
        PowerMockito.`when`(mockRealm.where(Cat::class.java)).thenReturn(catQuery)
        // when the RealmQuery is filtered on any string and any integer, return the query
        PowerMockito.`when`(
            catQuery.equalTo(
                ArgumentMatchers.anyString(),
                ArgumentMatchers.anyInt()
            )
        ).thenReturn(catQuery)
        // when a between query is performed with any string as the field and any int as the
        // value, then return the catQuery itself
        PowerMockito.`when`(
            catQuery.between(
                ArgumentMatchers.anyString(),
                ArgumentMatchers.anyInt(),
                ArgumentMatchers.anyInt()
            )
        ).thenReturn(catQuery)
        // When a beginsWith clause is performed with any string field and any string value
        // return the same cat query
        PowerMockito.`when`(
            catQuery.beginsWith(
                ArgumentMatchers.anyString(),
                ArgumentMatchers.anyString()
            )
        ).thenReturn(catQuery)
        // RealmResults is final, must mock static and also place this in the PrepareForTest
        // annotation array.
        PowerMockito.mockStatic(RealmResults::class.java)
        // create a mock RealmResults
        val cats = mockRealmResults<Cat>()
        // the for(...) loop in Java needs an iterator, so we're giving it one that has items,
        // since the mock RealmResults does not provide an implementation. Therefore, any time
        // anyone asks for the RealmResults Iterator, give them a functioning iterator from the
        // ArrayList of Cats we created above. This will allow the loop to execute.
        PowerMockito.`when`<Iterator<Cat>>(cats!!.iterator()).thenReturn(catList.iterator())
        // Return the size of the mock list.
        PowerMockito.`when`(cats.size).thenReturn(catList.size)
        // when we ask Realm for all of the Cat instances, return the mock RealmResults
        PowerMockito.`when`(mockRealm.where(Cat::class.java).findAll()).thenReturn(cats)
        // when we ask the RealmQuery for all of the Cat objects, return the mock RealmResults
        PowerMockito.`when`(catQuery.findAll()).thenReturn(cats)
        this.mockRealm = mockRealm
        this.cats = cats
    }
    @Test
    fun shouldBeAbleToAccessActivityAndVerifyRealmInteractions() {
        Mockito.doCallRealMethod().`when`(mockRealm)!!
            .executeTransaction(ArgumentMatchers.any(Realm.Transaction::class.java))
        // create test activity --  onCreate method calls methods that
        // query/write to realm
        val activity = Robolectric
            .buildActivity(UnitTestActivity::class.java)
            .create()
            .start()
            .resume()
            .visible()
            .get()
        // click the clean up button
        activity.findViewById<View>(R.id.clean_up).performClick()
        // verify that we queried for Cat instances five times in this run
        // (2 in basicCrud(), 2 in complexQuery() and 1 in the button click)
        Mockito.verify(mockRealm, Mockito.times(5))!!.where(Cat::class.java)
        // verify that the delete method was called. We also call delete at
        // the start of the activity to ensure we start with a clean db.
        Mockito.verify(mockRealm, Mockito.times(2))!!.delete(Cat::class.java)
        // call the destroy method so we can verify that the .close() method
        // was called (below)
        activity.onDestroy()
        // verify that the realm got closed 2 separate times. Once in the
        // AsyncTask, once in onDestroy
        Mockito.verify(mockRealm, Mockito.times(2))!!.close()
    }
    private fun <T : RealmObject?> mockRealmQuery(): RealmQuery<T>? {
        @Suppress("UNCHECKED_CAST")
        return PowerMockito.mock(RealmQuery::class.java) as RealmQuery<T>
    }
    private fun <T : RealmObject?> mockRealmResults(): RealmResults<T>? {
        @Suppress("UNCHECKED_CAST")
        return PowerMockito.mock(RealmResults::class.java) as RealmResults<T>
    }
}

Tip

See also:

See the Unit Testing Example App for an example of unit testing an application that uses Realm.

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