[ENH] unit tests for gen_imgs.py

[Yasserelhaddar]

Add Unit Tests for gen_imgs.py (Closes #387)

Summary

This PR addresses Issue #387 by adding comprehensive unit test coverage for the gen_imgs.py module, which generates visualization plots for pyGAM documentation.

Changes Made

Bug Fixes

• Fixed API compatibility issues in gen_imgs.py:
  • Updated gam.generate_X_grid() calls to include required term parameter
  • Fixed gam.partial_dependence() calls to use correct term and X arguments
  • Added robust lambda value extraction for gam.lam to handle nested arrays/lists

New Tests

• Added test_gen_imgs.py with unit tests for all plotting functions:
  • test_gen_basis_fns() - Tests basis function visualization
  • test_cake_data_in_one() - Tests cake data plotting
  • test_faithful_data_poisson() - Tests faithful data with Poisson distribution
  • test_single_data_linear() - Tests single data linear model
  • test_mcycle_data_linear() - Tests motorcycle data (2 plots)
  • test_wage_data_linear() - Tests wage data visualization
  • test_default_data_logistic() - Tests logistic regression
  • test_constraints() - Tests constraint visualization
  • test_trees_data_custom() - Tests custom tree data
  • test_gen_multi_data() - Tests multi-data generation (2 plots)
  • test_gen_tensor_data() - Tests tensor data visualization
  • test_chicago_tensor() - Tests Chicago tensor data
  • test_expectiles() - Tests expectile regression

Testing Strategy

• Unit Tests Only: Following pyGAM's existing test philosophy
• Mocked Dependencies: Uses mock.patch to isolate plt.savefig calls
• No File I/O: Prevents actual image generation during tests
• Fast Execution: Tests run quickly without complex model fitting
• Comprehensive Coverage: Tests all functions that generate plots

Test Results

>> pytest pyGAM/pygam/tests/test_gen_imgs.py -v
============================================= test session starts ==============================================
platform darwin -- Python 3.10.18, pytest-7.4.4, pluggy-1.6.0
rootdir: /Users/yasserelhaddar/opensource_contributions/pyGAM
plugins: cov-4.1.0
collected 13 items                                                                                             

pygam/tests/test_gen_imgs.py .............                                                               [100%]

======================================== 13 passed in 4.36s =========================================

Files Changed

• pyGAM/gen_imgs.py - API compatibility fixes
• pyGAM/pygam/tests/test_gen_imgs.py - New test file (created)

Why This Approach?

• Aligns with pyGAM conventions: Uses from mock import patch like other test files
• Maintains test isolation: No side effects or file system operations
• Follows existing patterns: Matches docstring style and test structure of other pyGAM tests
• Future-proof: Easy to extend with additional test cases

Related Issue

Closes #387 - "Add test coverage for gen_imgs.py"

---

Note: The API fixes in gen_imgs.py were necessary because the script was using outdated pyGAM method signatures. These fixes ensure the script works with the current pyGAM version while maintaining backward compatibility.

[fkiraly]

Great, thanks!

Very quickly before I review: the file has conflicts with the file on main, and is not passing code formatting checks. Please ensure you have checked with pre-commit.

[Yasserelhaddar]

Hey @fkiraly, Thanks for the feedback.
Both concerns are addressed.
Thank you !

[fkiraly]

Great! @dswah might like to review if this makes sense logic-wise.

Regarding folder structure, I think this might not exactly work - and it will have a broken import inside the package, since the root files are not packaged.

Could you put the test outside the package and ensure it is run there?

[dswah]

thanks @Yasserelhaddar !

[dswah]

@fkiraly do you see anything missing?

[Yasserelhaddar]

@dswah thanks for the feedback.
@fkiraly, I have restructured the test to be in root/test folder. They are also discoverable in the ci workflow.
Note: out of curiosity I ran the pre-commit hooks across all the files and I got over 800 Errors and linting inconsistencies. Maybe this needs your attention ?

[fkiraly]

No, all good from my side!

[fkiraly]

Note: out of curiosity I ran the pre-commit hooks across all the files and I got over 800 Errors and linting inconsistencies. Maybe this needs your attention ?

We only added pre-commit recently, so many of the files do not adhere to the stricter formatting. Fixing this would of course be appreciated, @Yasserelhaddar!