chore(java): write tests for most of the JavaIconProvider

[thelooter]

Warning

This PR depends on #145 getting merged before

Description

This PR introduces the following changes:

1. Added a new run configuration for running tests on the plugin project.
2. Updated the Gradle dependencies to include the Mockito Kotlin library for testing.
3. Added an internal getVisibilityIconForTesting method in the JavaIconProvider class to allow accessing the getVisibilityIcon method for unit testing purposes.
4. Added unit tests for the JavaIconProvider class to cover various scenarios for icon provision, including:
   • Testing visibility icon provision for different access modifiers (public, private, protected, package-private)
   • Handling cases where the requested element is not a PsiClass or the file is not a Java file
   • Testing the behavior when Java support is disabled in the plugin settings

Motivation and Context

The main goal of this PR is to improve the testability of the JavaIconProvider class in the Catppuccin JetBrains Icons plugin. The previous implementation did not provide a way to directly test the getVisibilityIcon method, which is an important part of the icon provision logic.

By adding the internal getVisibilityIconForTesting method and creating a comprehensive set of unit tests, we can ensure that the visibility icon provision works as expected, which will improve the overall reliability and maintainability of the plugin.

How Has This Been Tested?

This PR includes a new test suite for the JavaIconProvider class, which covers the various scenarios mentioned in the description. The tests ensure that the visibility icon provision logic works as expected for different access modifiers.

Checklist

• I have added tests to cover my changes.
• All new and existing tests passed.

[sgoudham]

Added an internal getVisibilityIconForTesting method in the JavaIconProvider class to allow accessing the getVisibilityIcon method for unit testing purposes.

Afaik, this is a bit of an anti-pattern when you create methods just for testing purposes in your production code. Does Kotlin not have visibility levels similar to Java?

[thelooter]

Added an internal getVisibilityIconForTesting method in the JavaIconProvider class to allow accessing the getVisibilityIcon method for unit testing purposes.

Afaik, this is a bit of an anti-pattern when you create methods just for testing purposes in your production code. Does Kotlin not have visibility levels similar to Java?

fixed

[kjnsn]

Please tidy up test descriptions ("Test" is redundant), and test method names