Add tests for record functions

[jakobnissen]

Also allow records with alignment length of zero.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 76.58%. Comparing base (7ef3eab) to head (e5d378c).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/PairwiseMappingFormat.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master       #2      +/-   ##
==========================================
+ Coverage   74.68%   76.58%   +1.89%     
==========================================
  Files           1        1              
  Lines         316      316              
==========================================
+ Hits          236      242       +6     
+ Misses         80       74       -6     

Flag	Coverage Δ
unittests	76.58% <0.00%> (+1.89%)	⬆️

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