ShouldNotBe is the inverse of ShouldBe.

Objects

ShouldNotBe works on all types and compares using .Equals.

var theSimpsonsCat = new Cat() { Name = "Santas little helper" };
theSimpsonsCat.Name.ShouldNotBe("Santas little helper");

Exception:

theSimpsonsCat.Name
    should not be
"Santas little helper"
    but was
"Santas little helper"

Want to contribute to Shouldly? #304 makes this error message better!

Numeric

ShouldNotBe also allows you to compare numeric values, regardless of their value type.

const int one = 1;
one.ShouldNotBe(1)

Exception:

one should not be 1 but was 1

const long aLong = 1L;
aLong.ShouldNotBe(1);

Exception:

aLong should not be 1 but was 1

ShouldNotBe DateTime overloads are similar to the numeric overloads and also support tolerances.

var date = new DateTime(2000, 6, 1);
date.ShouldNotBe(new DateTime(2000, 6, 1, 1, 0, 1), TimeSpan.FromHours(1.5));

Exception:

date
    should not be within
01:30:00
    of
01/06/2000 01:00:01
    but was 
01/06/2000 00:00:00

TimeSpan also has tolerance overloads

var timeSpan = TimeSpan.FromHours(1);
timeSpan.ShouldNotBe(timeSpan.Add(TimeSpan.FromHours(1.1d)), TimeSpan.FromHours(1.5d));

Exception:

timeSpan 
    should not be within
01:30:00
    of
02:06:00
    but was
01:00:00

Want to improve shouldy? We have an open issue at #303 to improve this error message!