@Test(expected = IllegalArgumentException.class)
public void observeInternetConnectivityShouldThrowAnExceptionWhenStrategyIsNull() {

  // given
  final InternetObservingStrategy strategy = null;
  final ErrorHandler errorHandler = new DefaultErrorHandler();
  // when
  ReactiveNetwork.observeInternetConnectivity(strategy, TEST_VALID_INITIAL_INTERVAL,
      TEST_VALID_INTERVAL, TEST_VALID_HOST, TEST_VALID_PORT, TEST_VALID_TIMEOUT,
      TEST_VALID_HTTP_RESPONSE, errorHandler);
  // then an exception is thrown
}