Instrumental test for Realm database gives "Call 'Realm.init(Context)' before creating Realmconfiguration" even though I call it

For my Android application I use the Realm mobile database. I want to write tests for this, and the best way I found of testing was using instrumental tests.

This is the constructor of my database class:

public Database(Context context) {
    this.context = context.getApplicationContext();

    Realm.init(context);

    RealmConfiguration realmConfig = new RealmConfiguration.Builder()
            .name("com.arnowouter.badger.realmdatabase") // TODO: 4/10/2016 check if encryptable
            .build();

    realm = Realm.getInstance(realmConfig);
}

As you can see, Realm.init(context) is called. But when I run this test:

@RunWith(AndroidJUnit4.class)
@MediumTest
public class DatabaseTest {

    Database database;
    Context context;

    @Before
    public void setupDatabase() {
        context = InstrumentationRegistry.getContext();
        database = new Database(context);
    }
}

I get this error:

java.lang.IllegalStateException: Call `Realm.init(Context)` before creating a RealmConfiguration
        at io.realm.RealmConfiguration$Builder.<init>(RealmConfiguration.java:399)
        at io.realm.RealmConfiguration$Builder.<init>(RealmConfiguration.java:394)
        at com.arnowouter.badger.Database.Database.<init>(Database.java:38)
        at com.arnowouter.badger.DatabaseTest.setupDatabase(DatabaseTest.java:27)
        at java.lang.reflect.Method.invoke(Native Method)
        at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
        at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
        at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
        at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)
        at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
        at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
        at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
        at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
        at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
        at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
        at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
        at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
        at org.junit.runners.Suite.runChild(Suite.java:128)
        at org.junit.runners.Suite.runChild(Suite.java:27)
        at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
        at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
        at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
        at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
        at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
        at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
        at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
        at org.junit.runner.JUnitCore.run(JUnitCore.java:115)
        at android.support.test.internal.runner.TestExecutor.execute(TestExecutor.java:59)
        at android.support.test.runner.AndroidJUnitRunner.onStart(AndroidJUnitRunner.java:262)
        at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1970)