Add tests for helper functions

[alexdewar]

Description

There isn't actually a lot of code in this repo (just helper functions to find and call the muse2 binary etc.), but what code we have should be tested -- coverage is currently at 48%.

Add tests for helper functions.

Closes #6.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.23%. Comparing base (d75a1f2) to head (30e8050).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #63       +/-   ##
===========================================
+ Coverage   47.61%   95.23%   +47.61%     
===========================================
  Files           3        3               
  Lines          42       42               
  Branches        4        4               
===========================================
+ Hits           20       40       +20     
+ Misses         22        1       -21     
- Partials        0        1        +1     

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[Copilot]

Pull request overview

This PR increases unit test coverage for the small set of helper utilities in muse2_data_analysis, focusing on locating the muse2 binary, invoking it via subprocess, and ensuring example input/output directories are prepared as expected.

Changes:

• Add tests for muse2.find_muse2() and muse2.run_muse2() (including success and failure paths).
• Add tests for helpers.get_example_input_dir() / helpers.get_example_output_dir() behavior when directories exist vs. need generating.
• Remove the (now unnecessary) tests/__init__.py.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
tests/test_muse2.py	Adds unit tests for binary discovery and subprocess invocation wrappers.
tests/test_helpers.py	Adds unit tests for example input/output directory helper functions.
tests/__init__.py	Removes the tests package marker file.

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