Add comprehensive testing and improvements for telegram filesystem

[slayer]

Summary

This PR adds comprehensive testing infrastructure and improvements to the telegram filesystem backend, achieving ~81% code coverage for production code.

Changes

🧪 Testing Infrastructure (New Files)

1. test_helpers.go (210 lines)

   • testLogger: Full logging implementation for tests with thread-safe log collection
   • MockBot: Mock Telegram bot interface (prepared for future mocking strategies)
   • Helper functions: createTestBot(), createTestAccess(), createTestAccessWithToken()

2. telegram_test.go (640 lines)

   • 22 comprehensive unit tests covering:
     • Fake filesystem operations and concurrency safety
     • File read/write operations with mutex protection
     • File extension matching (images, videos, audio, text)
     • Size limits and validation
     • Error conditions and edge cases

3. telegram_integration_test.go (392 lines)

   • 13 integration tests covering:
     • LoadFs parameter validation (empty token, invalid ChatID)
     • File extension detection for all supported types
     • File size validation (50MB Telegram limit)
     • Text size limit enforcement (4096 chars)
     • Filesystem operations (Create, Write, Read, Stat)
     • Multiple file creation workflows

🔧 Code Improvements

Error Handling

• Use os.ErrNotExist consistently in Stat() and LstatIfPossible()
• Add ErrFileTooLarge error for size limit violations
• Add UTF-8 validation for text files before sending to Telegram
• Proper error wrapping with context

Safety Features

• File size validation (50MB Telegram limit) in Write()
• Named constants: maxFileSize, maxTextSize, defaultDirSize
• Mutex protection for concurrent File read/write operations
• Graceful bot shutdown with Stop() method and channel signaling

Code Cleanup

• Remove dead code in fake_fs.go
• Add security warnings to bot command handlers
• Improve code documentation
• Better imports organization

🚀 CI/CD Improvement

• Clean up .github/workflows/build.yml by removing unnecessary apt-get command
• Add clarifying comment that GCC is pre-installed on ubuntu-24.04 runners

Test Results

Coverage

• Total Tests: 35 (13 new integration + 22 new unit tests)
• Status: ✅ All passing
• Race Detector: ✅ No race conditions detected
• Coverage: ~81% of production code (telegram.go, file_info.go, fake_fs.go)

Coverage Breakdown

fake_fs.go:      100.0% ✅
file_info.go:    100.0% ✅ 
telegram.go:      ~72% ✅

Note: Uncovered code (~19%) consists of:

• Actual Telegram Bot.Send() calls (require network/credentials)
• Bot command handlers (require complex test poller setup)
• LoadFs bot initialization with real token (requires network)

These are intentionally excluded from unit tests and should be tested manually or via E2E tests.

Testing Strategy

The tests follow a pragmatic approach using:

• Offline bot mode for testing LoadFs parameter validation
• In-memory fake filesystem for testing file operations without I/O
• Extension detection tests to verify correct file type routing
• Size validation tests to enforce Telegram limits
• Thread safety tests with race detector

This achieves high coverage without requiring actual Telegram credentials or network access.

Documentation

• Added TESTING_PROPOSAL.md with comprehensive testing strategy documentation (available locally, not committed to avoid clutter)

Breaking Changes

None. All changes are backward compatible.

Related Issues

Fixes the panic issue from commit a202228 and improves overall code quality and testability.

[Copilot]

Pull Request Overview

This PR adds comprehensive testing infrastructure and improvements to the telegram filesystem backend, achieving ~81% code coverage for production code. It introduces robust testing capabilities using offline bot mode and in-memory fake filesystem operations, while also improving error handling, safety features, and code organization.

• Implements comprehensive testing infrastructure with 35 unit and integration tests
• Adds safety features including file size validation and UTF-8 validation for text files
• Improves error handling with consistent os.ErrNotExist usage and proper error wrapping
• Introduces graceful bot shutdown mechanism and thread-safe file operations

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test_helpers.go	New test infrastructure with mock logger and bot implementations
telegram_test.go	New comprehensive unit tests covering filesystem operations and concurrency
telegram_integration_test.go	New integration tests for parameter validation and file type detection
telegram.go	Core improvements including safety features, error handling, and thread safety
file_info.go	Minor improvement replacing magic number with named constant
fake_fs.go	Code cleanup removing dead code comments
.github/workflows/build.yml	CI cleanup removing unnecessary apt-get command

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[slayer]

Additional Fix: Race Condition in Stop() Method

Added protection against multiple calls to Stop() to prevent panic on double-close of channel.

Changes:

• Added sync.Once field to Fs struct
• Modified Stop() to use sync.Once.Do() for idempotent shutdown
• Added TestFsStopMultipleCalls to verify thread-safe behavior

Why This Matters:

Calling Stop() multiple times on the same Fs instance would previously panic when trying to close an already-closed channel. With sync.Once, the cleanup code runs exactly once, making Stop() safe to call multiple times concurrently.

Test Results: ✅ All 36 tests passing with race detector

[Copilot]

Pull Request Overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Comments suppressed due to low confidence (1)

fs/telegram/telegram.go:1

• Add comments explaining these are Telegram's API limits to provide context for why these specific values are used.

// Package telegram provides a telegram access layer

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