Add test to assert errors are raised when returend by service
user
```ruby
describe 'Error' do

  it 'raises returned errors' do

    http_client = double(MessageBird::HttpClient)
    client = MessageBird::Client.new('', http_client)

    expect(http_client)
        .to receive(:request)
        .and_return('{"errors":[{"code": 2,"description": "Request not allowed (incorrect access_key)","parameter": "access_key"}]}')

    expect{client.message('some-id')}.to raise_error(MessageBird::ErrorException)
  end

end```
assistant