How to cover wth unit tests StreamWriter C#

How to test the next code sample?

using (StreamReader reader = new StreamReader(requestBody, Encoding.ASCII))
{
       ipnContext.RequestBody = reader.ReadToEnd();
}

The very first idea comes to my mind just create custom wrapper around StreamReader and inject it to class where it's needed. What do you thinks of it. Maybe you could give me more best solution. Thanks for your attention