ARC tests coverage

[jcbf]

I was looking at test coverage in this module and noted some low numbers. I was wondering if we could improve this number by adding Perl specific tests or it should be added to the suite?

lib/Mail/DKIM/ARC/MessageSignature.pm  100.0   81.2   60.0  100.0   66.6    0.6   91.0
lib/Mail/DKIM/ARC/Seal.pm              100.0   71.4  100.0  100.0   80.0    0.5   92.3
lib/Mail/DKIM/ARC/Signer.pm             56.5   45.3   24.2   56.5   68.7    0.3   51.7
lib/Mail/DKIM/ARC/Verifier.pm           88.7   78.6   67.6   94.1   22.2    2.8   82.4

PS : I will send a PR for the travis changes to enable coverage.

[marcbradshaw]

For sure, test coverage could be better. First step would be to enable coverage to get some visibility into the problem. coveralls.io?

[jcbf]

I got my fork there . I'll create a PR for the travis.yml changes and then create tests for the missing coverage, mainly for the ARC part.

At the first glance stuff related with "using default values" is missing.