How to test a web service with different configurations?

Question

I want to automatically test http://localhost/api.ashx.

api.ashx reads configurations from web.config and acts differently.

For example one key is AllowDuplicatedQueryParameter. If web.config has

<appSettings>
  <add key="AllowDuplicatedQueryParameter" value="false" />
</appSettings>

requesting to http://localhost/api.ashx?name=hello&name=world will throw error.

How do I have an automated test that tests different configurations, namely when AllowDuplicatedQueryParameter=true and AllowDuplicatedQueryParameter=false?

Answer 1

It depends a bit on what kind of automated testing you want to do. Under the circumstances, unit testing or integration testing against a in-process version of your application seems like it would make sense.

Your best option in these cases is to abstract the reading of the configuration into a class that can be mocked. For example, imagine the configuration you change is in your AppSettings you might do something similar to this

public interface IConfigurationWrapper
{
    string GetAppSetting(string key);
}

public class ConfigurationWrapper : IConfigurationWrapper
{
     public string GetAppSetting(string key)
     {
         return ConfigurationManager.AppSettings[key]
     }
}

Your components should take a dependency on an
IConfigurationWrapper, and use it whenever you need to access configuration to determine behavior. In your test, you can use a mocking library like Moq or NSubstitute, or roll your own stub implementation of the IConfigurationWrapper and use that to controll the behavior of the system under test, like this:

public class MyThingDoer
{
    public MyThingDoer(IConfigurationWrapper config)
    {
         _config = config
    }

    public string SaySomething()
    {
        var thingToSay = _config.GetAppSetting("ThingToSay");
        return thingToSay;
    }
}

And then in your test

[Fact]
public void ThingDoerSaysWhatConfigTellsItToSay()
{
    var configWrapper = new FakeConfigWrapper(thingToSay:"Hello");
    var doer = new MyThingDoer(configWrapper);
    Assert.Equal("Hello", doer.SaySomething());
}

Obviously that's a toy example, but it should get at the basic idea. Write an abstraction around the external dependency, then stub the dependency.