public void Run() { var stub = new FormattableStub(123); AssertionFailure[] failures = Capture(() => Assert.IsNull(stub)); Assert.Count(1, failures); var actualValue = failures[0].LabeledValues.Single(x => x.Label == "Actual Value"); Assert.AreEqual("CustomFormatter: FormattableStub's value is 123.", actualValue.FormattedValue.ToString()); }