Use an in-memory database when running instrumented tests.

- added new TestRunner and new TestApplication
- The TestRunner loads TestApplication as the apps Application instance when running the tests
- added new interface AppConfig to retrieve the database name
- changed Startup (Application) so that it implements AppConfig
- changed CustomSQLiteOpenHelper so that it retrieves the database name from the Application instance
- Startup provides the production database name
- TestApplication provides null which yields an in-mememory database

src/androidTest/java/de/dennisguse/opentracks/TestApplication.java

@@ -0,0 +1,9 @@
+package de.dennisguse.opentracks;
+
+public class TestApplication extends Startup {
+    @Override
+    public String getDatabaseName() {
+        // null will make SQLiteOpenHelper create an in-memory database
+        return null;
+    }
+}

src/androidTest/java/de/dennisguse/opentracks/TestRunner.java

@@ -0,0 +1,14 @@
+package de.dennisguse.opentracks;
+
+import android.app.Application;
+import android.content.Context;
+
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import androidx.test.runner.AndroidJUnitRunner;
+
+public class TestRunner extends AndroidJUnitRunner {
+    @Override
+    public Application newApplication(ClassLoader cl, String className, Context context) throws ClassNotFoundException, IllegalAccessException, InstantiationException {
+        return super.newApplication(cl, TestApplication.class.getName(), context);
+    }
+}

src/androidTest/java/de/dennisguse/opentracks/services/TrackRecordingServiceTest.java

@@ -71,9 +71,6 @@ import de.dennisguse.opentracks.settings.PreferencesUtils;
  * Tests for the track recording service.
  *
  * @author Bartlomiej Niechwiej
- * <p>
- * //TODO ATTENTION: This tests deletes all stored tracks in the database.
- * So, if it is executed on a real device, data might be lost.
  */
 @RunWith(AndroidJUnit4.class)
 public class TrackRecordingServiceTest {

src/androidTest/java/de/dennisguse/opentracks/services/TrackRecordingServiceTestLocation.java

@@ -41,9 +41,6 @@ import static org.junit.Assert.assertFalse;
 
 /**
  * Tests insert location.
- * <p>
- * //TODO ATTENTION: This tests deletes all stored tracks in the database.
- * So, if it is executed on a real device, data might be lost.
  */
 @RunWith(AndroidJUnit4.class)
 //TODO Implement as mock test; no need to store data in database

src/androidTest/java/de/dennisguse/opentracks/services/TrackRecordingServiceTestLooper.java

@@ -43,9 +43,6 @@ import static org.junit.Assert.assertTrue;
  * Tests for the track recording service, which require a {@link Looper}.
  *
  * @author Bartlomiej Niechwiej
- * <p>
- * ATTENTION: This tests deletes all stored tracks in the database.
- * So, if it is executed on a real device, data might be lost.
  */
 @RunWith(AndroidJUnit4.class)
 public class TrackRecordingServiceTestLooper {