Fix: repair ignored test files

[payalrvs3]

Description

Repairs all 5 test files that were silently ignored in CI, as reported in #804. Each fix targets the root cause rather than patching symptoms.

Changes made

File	What changed
backend/requirements.txt	Added beautifulsoup4, flask-caching, vaderSentiment
backend/cache_service.py	Split redis/flask_caching imports into separate try blocks; added Cache = None fallback and early-return guard so caching degrades gracefully when flask-caching is absent
tests/conftest.py	Added stubs for magic, spine_generator, vaderSentiment, vaderSentiment.vaderSentiment, nltk.corpus so tests run on Windows and without optional native libraries
tests/test_purchase_links.py	Removed module-level from app import app and local client fixture that caused a double-import of backend/app.py, producing a broken second Flask instance and 404 responses; now uses conftest's properly-initialised client
tests/test_env_validation.py	Replaced os.environ.clear() + manual restore pattern with monkeypatch.setenv/delenv and monkeypatch.delitem(sys.modules, 'config') for proper per-test isolation
tests/test_llm.py	Full rewrite - original file had only print statements and collected 0 pytest items; replaced with TestIsAvailable, TestGenerateText, and TestLLMServiceSingleton classes using mocks
.github/workflows/ci.yml	Added flask-caching to install step; removed 5 --ignore flags so all repaired tests run in CI

Root causes fixed

• test_mood_cache_db: beautifulsoup4 and vaderSentiment installed ad-hoc in CI but missing from requirements.txt
• test_category_cache: redis and flask_caching were in the same try block - import redis failing meant Cache was never defined, disabling caching entirely and breaking cache-hit assertions
• test_purchase_links: from app import app at module level created a second Flask instance (sys.modules['app'] vs sys.modules['backend.app']), corrupting SQLAlchemy state → 404
• test_env_validation: os.environ.clear() wiped system env vars mid-test; no sys.modules isolation between tests leaked stale config state
• test_llm: File contained only print() statements - not a pytest test at all

Related Issue

Fixes #804

Type of Change

• Bug Fix

Testing

Ran full test suite locally:

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[mayank-dev-15]

Good fix - repairing ignored test files ensures test coverage is maintained. LGTM.

[RudraMalvankar]

Thanks for working on re-enabling the previously ignored test suites.

The overall direction looks good and the added test coverage is valuable. I left a comment regarding the cache initialization path in cache_service.py, as it may lead to self.cache being unset when flask-caching is unavailable.

Other than that, the test cleanup and CI updates look reasonable.

[RudraMalvankar]

Returning early here leaves self.cache unset. Downstream code that assumes self.cache exists may raise an AttributeError. Would it be safer to initialize a fallback cache implementation or explicitly set self.cache = None before returning?

[payalrvs3]

@RudraMalvankar, Thanks for looking closely! self.cache is already initialised to None in __init__ before init_app is ever called, so the early return leaves it in the same state it would be in if we assigned it explicitly. Every downstream method (get, set, delete) also guards with if not self.cache: return None/False, so there's no AttributeError risk. Happy to add the explicit assignment if you'd prefer it for readability, but the behaviour is identical either way.