Add a new test for sAHP extraction

[AurelienJaquier]

Motivation: sAHP has two amplitudes, amp and amp2, which was not tested with current tests (only extracting for IDRest)

• add init in tests folder so that we can fetch functions from other files, and exclude tests folder in setup find_packages, so that pypi does not make user download tests as a module, now that it has an init file in it.

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (d4edc58) 65.95% compared to head (d54e131) 70.22%.

Files	Patch %	Lines
tests/test_extractor.py	97.67%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #163      +/-   ##
==========================================
+ Coverage   65.95%   70.22%   +4.26%     
==========================================
  Files          34       35       +1     
  Lines        2159     2223      +64     
==========================================
+ Hits         1424     1561     +137     
+ Misses        735      662      -73     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[ilkilic]

Well done, looks good!