IT:AD:FluentAssertions

The library works equally well with IT:AD:NUnit as IT:AD:XUnit as well other frameworks – so it makes your tests portable (bar the Test/Fact attributes which have to be updated).

The library uses a Should() method followed by one of a set of Be...() methods, which makes your tests very readable:

var foo = false;
foo.Should().BeTrue();

var bar = 3;
foo.Should().Be(3);
foo.Should().BeGreaterThan(2);
foo.Should().BeLessThan(4);
foo.Should().NotBe(5);