Test suite & fixes for validate package

[twitchyliquid64]

I've started working through the official test suite and representing the tests specified in there as tests on the validate module.

As I go, I'm fixing any issues I find.

[codecov-io]

Codecov Report

Merging #161 into master will decrease coverage by 0.1%.
The diff coverage is 66.12%.

@@            Coverage Diff             @@
##           master     #161      +/-   ##
==========================================
- Coverage   69.72%   69.61%   -0.11%     
==========================================
  Files          43       48       +5     
  Lines        5010     5466     +456     
==========================================
+ Hits         3493     3805     +312     
- Misses       1221     1317      +96     
- Partials      296      344      +48

Impacted Files	Coverage Δ
validate/error.go	0% <0%> (ø)
validate/vm.go	84.15% <71.42%> (ø)
validate/validate.go	68.86% <90%> (ø)
validate/log.go	66.66% <0%> (ø)
validate/operand.go	100% <0%> (ø)

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[twitchyliquid64]

Okay, I think thats a good amount of tests for one PR. Feel free to review at your leisure (no rush 😄 ).

[sbinet]

LGTM.

only a couple of nit-picks.
thanks!

[twitchyliquid64]

@sbinet this is ready, but the two new PR checks are failing ... what are they? can we skip them?

[sbinet]

yeah, codecov is being a bit too stringent (and speaks up when the code coverage drops by some tiny margin.)
not sure how to change that...