Testing a private field using MSTest

Question

Is it possible to get access to a private field in a unit test?

Answer 1

The way to get private fields or methods in general is to use Reflection. However, the unit test framework includes a helper class, PrivateObject, to make this easier. See the docs. In general, when I've used this, I've ended up making an extension methods like the following:

public static int GetPrivateField(this MyObject obj)
{
  PrivateObject po = new PrivateObject(obj);
  return (int)po.GetField("_privateIntField");
}

If you need to get private fields in a static class, however, you will need to go with straight up reflection.

Answer 2

Nice solution offered above. For completeness, I have been using this technique for a while now (using MSTest), but have extended it for property values also.

[ExcludeFromCodeCoverage]
public static class TestExtensionMethods
{
    public static T GetFieldValue<T>(this object sut, string name)
    {
        var field = sut
            .GetType()
            .GetField(name, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);

        return (T)field?.GetValue(sut);
    }

    public static T GetPropertyValue<T>(this object sut, string name)
    {
        var field = sut
            .GetType()
            .GetProperty(name, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);

        return (T)field?.GetValue(sut);
    }
}