gistfile1.cs

[Test]
public void ExpressionsWithChildrenShouldOverrideVisitMethod()
{
    var expressionTypes = typeof(IExpression)
        .Assembly.GetTypes()
        .Where(t => typeof(IExpression).IsAssignableFrom(t))
        .Where(t => !t.IsInterface);

    var withChildren = expressionTypes
        .Where(t => t.GetFields(BindingFlags.Instance |
                BindingFlags.Static |
                BindingFlags.NonPublic |
                BindingFlags.Public)
                .Any(f => typeof(IExpression).IsAssignableFrom(f.FieldType)));

    var withChildrenAndNoVisitOverride = withChildren
            .Where(t => t.GetMethod("Visit").DeclaringType != t)
            .Select(t => t.Name)
            .ToArray()
                ;

    if (withChildrenAndNoVisitOverride.Length > 0)
    {
        string names = withChildrenAndNoVisitOverride.Length > 1 ?
            withChildrenAndNoVisitOverride.Aggregate((a, b) => string.Format("{0}, {1}", a, b)) :
            withChildrenAndNoVisitOverride.First();

        Assert.Fail(string.Format("Expressions with children ({0}) should override the Visit method",
            names));
    }
}