public void ProvidesPartsOfBuiltin() { using (var fake = new AutoSubstitute()) { var bar = fake.ProvidePartsOf <IBar, Bar>(); bar.When(x => x.Fuzz()).DoNotCallBase(); bar.Fuzz().Returns("Fuzz"); var foo = fake.Resolve <Foo>(); var result = foo.Fuzz(); Assert.Equal("Fuzz", result); } }