Add matcher for length of a sequence

[Andrew Bennetts]

bzrlib has a nice assertLength helper which helpfully shows the contents of the sequence if the length is not the expected value. But it's not a matcher, so for more complex cases tests resort to ad hoc assertions that look like:

    if len(self.hpss_calls) < 34 and len(self.hpss_calls) > 47:
        self.fail("Expected hpss_calls to have between 34 and 47 elements, got %d (%r)"
            % (len(self.hpss_calls), self.hpss_calls))

It would be nice if there were a matcher for this, so that could be written like:

    self.assertThat(
        self.hpss_calls, Length(MatchesAny(LessThan(34), GreaterThan(47))))

(And so get the nice formatted errors etc for free.)

[Jonathan Lange (jml)]

On Tue, Dec 6, 2011 at 2:11 AM, Andrew Bennetts
<email address hidden> wrote:
> Public bug reported:
>
> bzrlib has a nice assertLength helper which helpfully shows the contents
> of the sequence if the length is not the expected value.  But it's not a
> matcher, so for more complex cases tests resort to ad hoc assertions
> that look like:
>
>    if len(self.hpss_calls) < 34 and len(self.hpss_calls) > 47:
>        self.fail("Expected hpss_calls to have between 34 and 47 elements, got %d (%r)"
>            % (len(self.hpss_calls), self.hpss_calls))
>
> It would be nice if there were a matcher for this, so that could be
> written like:
>
>    self.assertThat(
>        self.hpss_calls, Length(MatchesAny(LessThan(34), GreaterThan(47))))
>
> (And so get the nice formatted errors etc for free.)

Cheapest way to do this:

  Length = lambda matcher: AfterPreprocessing(len, matcher)

jml