Negation

Almost every expectation has a negated counterpart that starts with IsNot… or DoesNot…, e.g. IsNotEqualTo, DoesNotContain or DoesNotStartWith. The Has… properties take a negated comparison instead, e.g. HasLength().NotEqualTo(9), and the quantifiers of a collection use None(). The table at the top of each reference page lists the negated counterparts.

DoesNotComplyWith negates any expectation, including your own:

string title = "Abbey Road";

await Expect.That(title).DoesNotComplyWith(it => it.StartsWith("Let").And.EndsWith("Be"));

DoesNotComplyWith is the exact inverse: it succeeds as soon as the nested expectation fails. A named negation can be stricter, e.g. DoesNotContainKeys fails as soon as any of the keys is contained, while DoesNotComplyWith(d => d.ContainsKeys(…)) only fails when all of them are.

A null subject fails most expectations and their negations alike, see null subjects.