Category: Test

InternalsVisibleTo usage

I do not know if you know  InternalsVisibleToAttribute

https://msdn.microsoft.com/en-us/library/system.runtime.compilerservices.internalsvisibletoattribute%28v=vs.110%29.aspx?f=255&MSPPError=-2147217396  .

I have used on a project https://github.com/ignatandrei/WorldBankAPi , that deals with World Bank API to get information

Let’s take an example: Countries: http://api.worldbank.org/countries?format=json

I have had a class CountriesRepository, that deals with transforming countries Json from WorldBank to Country classes. How can I test it WITHOUT relying on reading data from the internet ?

Simple:

1. Make an interface to grab JSON , IJSonData

    public interface IJsonData
    {
        Task<string> JsonData(int page = 1);
    }

2. Make a class JSONCountry that reads JSON from HTTP and implements IJSonData

3.  Make the CountryRepository class with 2 constructors  – one with IJSonData and the default calling JSONCountry

[assembly: InternalsVisibleTo("WorldBank.Test")]
namespace WorldBank.Repository
{
    public class CountriesRepository
    {
        private IJsonData data;
        public CountriesRepository():this(new JsonCountries())
        {

        }
//this is internal - could not see by outside projects with exception of WorldBank.Test
//see InternalsVisibleTo above
        internal CountriesRepository(IJsonData data)
        {
            this.data = data;
        }
    }
}

Optional: when testing manually, save the json into same files on the hard disk – you will need for point 5

4. The code that will use CountryRepository in official way will use the default – will not see the one with IJSonData

var c = new CountriesRepository();
var data = c.GetCountries().Result;

5. The testing code will define another class JSONFromHard that implements IJSonData and reads data from Hard

class JsonFromHard : IJsonData
{
//code to read files from disk 
// you have saved those when testing manually 
//see point 2 the optional part 
}

6. Because I have defined InternalsVisibleToAttribute to the WorldBank.Test, the Test dll can see the constructor with IJSonData  and then it class with JSONFromHard   – and I have no dependecy on the Http

 

public void GetAndInterpretData()
        {
            //uses [assembly: InternalsVisibleTo("WorldBank.Test")]
            var c = new CountriesRepository(new JsonFromHard("Countries"));
            var data = c.GetCountries().Result;
            Assert.Equal(218, data.Length);
        }

You can download the project from https://github.com/ignatandrei/WorldBankAPi  to see working.

Andrei Ignat weekly software news(mostly .NET)

* indicates required

Please select all the ways you would like to hear from me:

You can unsubscribe at any time by clicking the link in the footer of our emails. For information about our privacy practices, please visit our website.

We use Mailchimp as our marketing platform. By clicking below to subscribe, you acknowledge that your information will be transferred to Mailchimp for processing. Learn more about Mailchimp's privacy practices here.