@Test
public void testClose() {

    final B2AccountAuthorizer authorizer = mock(B2AccountAuthorizer.class);
    final B2ClientConfig config = mock(B2ClientConfig.class);
    when(config.getAccountAuthorizer()).thenReturn(authorizer);
    final B2StorageClientImpl client = new B2StorageClientImpl(webifier, config, B2DefaultRetryPolicy.supplier());
    // closing the client should close the config the first time.
    client.close();
    verify(webifier, times(1)).close();
    // closing the client should do nothing the second time.
    client.close();
    verify(webifier, times(1)).close();
}