dify - 💡(How to fix) Fix [Refactor/Chore] Improve Service Layer Test Coverage and Fix Discovered Bugs [2 pull requests]

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Description

Summary

While working on improving the test coverage for modules in the services directory (specifically those with <= 20% coverage), I discovered and fixed two bugs in the business logic.

This issue tracks the effort to both fix these bugs and contribute the full suite of new unit tests, which significantly increases the stability and maintainability of the service layer.

Discovered Bugs

1. Bug in services/app_dsl_service.py:

   • Issue: The AppDslService.import_app method, when using the YAML_CONTENT import mode, lacked content size validation. This was inconsistent with the YAML_URL mode, which already enforced the DSL_MAX_SIZE limit. This could lead to memory pressure, OOM errors, or service hangs when importing oversized YAML content.
   • Fix: Added a consistent content length validation against DSL_MAX_SIZE for the YAML_CONTENT mode.

2. Bug in services/plugin/plugin_migration.py:

   • Issue: The plugin existence check logic during installation was broken in two ways:
     1. Wrong dictionary access: It used plugins.get(plugin_id) instead of the correct path plugins["plugins"].get(plugin_id).
     2. Reversed condition: It was incorrectly adding already existing plugin IDs to the plugin_not_exist list.
   • Fix: Corrected the dictionary lookup path for the plugin identifier and fixed the logical condition to correctly identify and record only the truly missing plugins.

Plan of Action

To ensure a clear and efficient review process, I will submit two separate Pull Requests:

1. PR #36072: Will contain the fixes for the two bugs described above, along with their corresponding unit tests (test_app_dsl_service.py and test_plugin_migration.py).
2. PR #36074: Will submit the remaining unit tests for the other 8 low-coverage service modules.

Both PRs will be linked to this issue for complete tracking.

Motivation

No response

Additional Context

<img width="960" height="441" alt="Image" src="https://github.com/user-attachments/assets/6448da4f-10b4-4266-b5b4-abf70f22b8ff" />