What is Correct way to get ActivityContext in instrumentedtestcase for testing sqlite based API's?

I have DatabaseManager Class as below

public class DatabaseManager {

    private AtomicInteger mOpenCounter = new AtomicInteger();
    private static DatabaseManager instance;
    private static MySQLiteOpenHelper mDatabaseHelper;
    private SQLiteDatabase mDatabase;

    private static final String DB_NAME = "KVStore";
    private static final String TABLE_NAME = "master";
    public static final String COLUMN_KEY = "Key";
    public static final String COLUMN_VALUE ="Value";

    private static final int DB_VERSION = 1;

    //Initialize DBManager Instance
    public static synchronized void initializeInstance(MySQLiteOpenHelper helper) {
        if (instance == null) {
            instance = new DatabaseManager();
            mDatabaseHelper = helper;
        }
    }

    //Get DBManager Instance
    public static synchronized DatabaseManager getInstance() {
        if (instance == null) {
            throw new IllegalStateException(DatabaseManager.class.getSimpleName() +
                    " is not initialized, call initializeInstance(..) method first.");
        }

        return instance;
    }
    //Open DB for Read/Write
    public synchronized SQLiteDatabase openDatabase() {
        if(mOpenCounter.incrementAndGet() == 1) {
            // Opening new database
            mDatabase = mDatabaseHelper.getWritableDatabase();
        }
        return mDatabase;
    }
    //Close DB
    public synchronized void closeDatabase() {
        if(mOpenCounter.decrementAndGet() == 0) {
            // Closing database
            mDatabase.close();

        }
    }

// MySQLiteOpenHelper

    public static class MySQLiteOpenHelper extends SQLiteOpenHelper {

        public MySQLiteOpenHelper(Context context) {

            super(context, DB_NAME, null, DB_VERSION);
        }

        public void onCreate(SQLiteDatabase sqLiteDatabase) {
            sqLiteDatabase.execSQL("create table " + TABLE_NAME +"("+COLUMN_KEY+" TEXT primary key,"+COLUMN_VALUE+" TEXT )");
        }

        public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldv, int newv) {
            sqLiteDatabase.execSQL("DROP TABLE IF EXISTS "+ TABLE_NAME);
            onCreate(sqLiteDatabase);
        }
    }

}

And KVStoreWrapper class as below:

public class KVStoreWrapper {

    static  SQLiteDatabase database;
    static String key,value;
    //Add new Key, Value entry
    public  void addEntry(String key,String value)
    {
        database = DatabaseManager.getInstance().openDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put("Key",key);
        contentValues.put("Value",value);
        database.insertOrThrow("master", null, contentValues);
        DatabaseManager.getInstance().closeDatabase();
    }
    public  void addIntEntry(String key,int value)
    {
        database = DatabaseManager.getInstance().openDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put("Key",key);
        contentValues.put("Value",value);
        database.insertOrThrow("master", null, contentValues);
        DatabaseManager.getInstance().closeDatabase();
    }

}

And my instrumented test class is below:

import android.content.Context;
import android.os.Handler;
import android.support.test.runner.AndroidJUnit4;
import android.test.InstrumentationTestCase;
import android.test.suitebuilder.annotation.SmallTest;
import org.junit.Test;
import org.junit.runner.RunWith;
@RunWith(AndroidJUnit4.class)
@SmallTest
public class KVStoreTest extends InstrumentationTestCase {
    private TestActivity ha;
    private KVStoreWrapper kvsw;
    Handler mHandler;

    @Test
    public void testAddRetrieveEntry() {
        Context context = this.getInstrumentation().getTargetContext().getApplicationContext();
        DatabaseManager.MySQLiteOpenHelper myDBHelper=new DatabaseManager.MySQLiteOpenHelper(context);
        DatabaseManager.initializeInstance(myDBHelper);

        kvsw=new KVStoreWrapper();
        String key="Key";
        String value="Value";
        kvsw.addEntry(key, value);
        String retrievedValue=kvsw.retrieveEntry(key);
        assertEquals("Conversion from celsius to fahrenheit failed",value,
            retrievedValue);

    }
}

But I get error

java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' on a null object reference

What is correct way to get activity context to test sqlite based api's.