Indicate Positive or Negative Behaviour
All good test suites include both positive and negative tests. Behaviour Specifications are the same in this regard.
Positive Testing should ensure that the functionality under test works as expected, produces expected errors as required, and does not produce unexpected errors.
Negative Testing should ensure that the functionality under test can gracefully handle an unexpected or invalid circumstance that causes the functionality to break.
In my experience, prefixing the Behaviour Specification Description (before the word "
Should") with "
Positive" or "
Negative" allows everyone reading the Behaviour Specification or test report to quickly and easily understand whether the behaviour is focused on the positive or negative situation.