Rework e2e tests to be included in coverage

[juliaogris]

Fixes #71 .

Changes proposed in this pull request:

• rework sysl.main to take argument as optional (default sys.argv[1:]) parameter for testing
• extend e2e tests to optionally directly call sysl.main rather than start a subprocess

@anz-bank/sysl-developers

[codecov]

Codecov Report

Merging #73 into master will increase coverage by 1.64%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master      #73      +/-   ##
==========================================
+ Coverage   55.74%   57.39%   +1.64%     
==========================================
  Files          36       36              
  Lines        7037     7037              
==========================================
+ Hits         3923     4039     +116     
+ Misses       3114     2998     -116

Impacted Files	Coverage Δ
src/sysl/core/__main__.py	77.02% <66.66%> (+77.02%)	⬆️
src/sysl/core/syslints.py	82.78% <0%> (+3.27%)	⬆️
src/sysl/core/sysldata.py	85.32% <0%> (+4.58%)	⬆️
src/sysl/core/syslseqs.py	14.11% <0%> (+14.11%)	⬆️
src/sysl/util/argparse.py	100% <0%> (+76.92%)	⬆️

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[sahejsingh]

why do you need subprocess=True calls?

[juliaogris]

I suppose I want true "end-to-end" tests from an enduser perspective, who doesn't care wether the program was written in Python or anything else.
Eventually we might swap out the executables underneath but the tests should remain the same (at least the subprocess=True ones).
It also covers cases where the command line operates unexpectedly different from calling main directly.
Does any of this convince you?

[sahejsingh]

Yup. thanks!