Motivation

Currently, test cases in optuna/visualization/matplotlib/*.py are not enough comparing to optuna/visualization/*.py. For example, in the case of optuna/visualization/matplotlib/edf.py, we should check the number of lines and titles of each figure as we fixed them in #2642.

Description

• test_contour.py (Added unit tests for contour of matplotlib tests #2806)
• test_edf.py (Add test cases in optuna/visualization/matplotlib/edf.py #2642)
• test_intermediate_plot.py (Add specific test cases for visualization.matplotlib.plot_intermediate_values #2754)
• test_optimization_history.py (Added unit tests for optimization history of matplotlib tests #2761)
• test_parallel_coordinate.py (Changed unit tests for parallel coordinate of matplotlib tests #2778)
• test_param_importances.py (Added unit tests for param importances of matplotlib tests #2774)
• test_pareto_front.py (Changed unit tests for pareto front of matplotlib tests #2763)
• test_slice.py (Added unit tests for slice of matplotlib tests #2764)