Fix bug #543: Unstable behavior in PredictRating()

[ngtduc693]

Related issue

#543 Unstable behavior in PredictRating() unit test due to constructor field shadowing

Affected module

• CollaborativeFilteringTests.cs

Root Cause

The instability was not caused by the algorithm itself, but by the test fixture design:

• The test then fails intermittently, even though the same code passes when executed in isolation
• When the entire test suite runs in parallel, other tests’ [SetUp] methods overwrite these fields while this test is still executing.
• The mock that should return a fixed similarity (.Returns(0.8)) is replaced mid-run by a fresh, unconfigured instance, causing:

similarity = 0
PredictRating() → total similarity ≈ 0 → result = 0

Fix Summary

Use the [NonParallelizable] flag

Unit Test Passed Evidence

• I have performed a self-review of my code
• My code follows the style guidelines of this project
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Comments in areas I changed are up to date
• I have added comments to hard-to-understand areas of my code
• I have made corresponding changes to the README.md

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.67%. Comparing base (7467fe4) to head (7b4fc36).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #544      +/-   ##
==========================================
- Coverage   96.67%   96.67%   -0.01%     
==========================================
  Files         279      279              
  Lines       11015    11013       -2     
  Branches     1568     1568              
==========================================
- Hits        10649    10647       -2     
  Misses        232      232              
  Partials      134      134              

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[siriak]

Please resolve conflicts

[ngtduc693]

Please resolve conflicts

I'm done, thanks @siriak