TestUtil.java

// Resets keyspace by truncating all tables in keyspace. 
//
// session is an Rx wrapper around com.datastax.driver.core.Session and
// and uses the async methods in Session. The execute method return an
// Observable<ResultSet>.
public void truncateTables(String keyspace) {
    session.execute("select table_name from system_schema.tables where keyspace_name = '" + keyspace + "'")
            .flatMap(Observable::from)
            .flatMap(row -> session.execute("truncate " + row.getString(0)))
            .toCompletable()
            .await(10, TimeUnit.SECONDS);
}