public void assert_equal()
 {
     Assertion.Equal(string.Empty, string.Empty);
     Assert.Throws <ArgumentException>(() => Assertion.Equal(null, null));
     Assert.Throws <ArgumentException>(() => Assertion.Equal(null, new object()));
     Assert.Throws <ArgumentException>(() => Assertion.Equal(new object(), null));
     Assert.Throws <ArgumentException>(() => Assertion.Equal(new object(), new object()));
 }