public void TestWeakerPrecondition()
{
// Code contracts does not support preconditions in derived types,
// so this test will fail with precondition violation and
// static checker warns us about it!
var d = new Derived();
d.Foo("");
}
public void TestStrongerPostcondition()
{
var d = new Derived();
var r = d.Foo("42");
Assert.IsInstanceOf<string>(r);
}