[MRG+1] Various FormRequest tests+fixes

[Digenis]

#1595 FormRequest should consider input type values case-insensitive
#1596 FormRequest doesn't handle input elements without type attribute

Plus: I noticed a maybe-unicode xpath wasn't encoded
when raising an exception whose str message is formatting it with %s.

[codecov-io]

Current coverage is 82.76%

Merging #1597 into master will increase coverage by +0.03% as of 9a30a3d

Powered by Codecov. Updated on successful CI builds.

[kmike]

Awesome, thanks!

[redapple]

lxml has support for EXSLT regex extensions:
https://stackoverflow.com/questions/2755950/how-to-use-regular-expression-in-lxml-xpath
http://exslt.org/regexp/functions/test/index.html

boolean regexp:test(string, string, 'i')

I think it would be easier to read

[Digenis]

re:test(@type, "^(submit|image|reset)$", "i") only for the first 3
and separately the checkbox and the radio.
Alternatively it's a regexp per value.
I didn't test it but I think there should be a performance penalty
invoking python's re module instead of leaving it to libxml.

[redapple]

" there should be a performance penalty"
probably. I'd be curious to see a comparison.

and I'd still go for the regexp version for readability

[Digenis]

I changed it according to @redapple's suggestion.
Is there anything else left for this PR?

[kmike]

@redapple what do you think about the new implementation?

[redapple]

@Digenis , @kmike ,
looks alright to me,
although the ../@checked part feels a bit odd.
But more correct now than before (I mean before the PR)
so LGTM

FWIW, I was thinking of something like

inputs = form.xpath(r'''descendant::textarea |
                        descendant::select |
                        descendant::input[not(
                            @type and
                            (
                                re:test(@type, "^(submit|image|reset)$", "i") or
                                (not(@checked) and re:test(@type, "^(checkbox|radio)$", "i"))
                            )
                        )]''',
                    namespaces={"re": "http://exslt.org/regular-expressions"})

[Digenis]

Is there something left to do for this PR?