Guids
The assertions you can do on Guids are simple. You can assert their equality to another Guid, or you can assert that a Guid is empty.
Guid theGuid = Guid.NewGuid();
Guid sameGuid = theGuid;
Guid otherGuid = Guid.NewGuid();
theGuid.Should().Be(sameGuid);
theGuid.Should().NotBe(otherGuid);
theGuid.Should().NotBeEmpty();
Guid.Empty.Should().BeEmpty();
theGuid.Should().Be("11111111-aaaa-bbbb-cccc-999999999999");
theGuid.Should().NotBe("00000000-0000-0000-0000-000000000001");