docs: add comprehensive testing documentation

- Add TESTING.md with complete overview of GitHub Actions testing suite
- Document all 4 new workflows and their coverage areas
- Detail v1.5.0 specific testing including version commands, cross-platform compatibility, and enhanced error handling
- Explain platform coverage (macOS, Ubuntu, Linux containers) and test categories
- Provide maintenance guidelines and usage instructions for contributors and maintainers
- Document 823 lines of workflow configuration ensuring comprehensive quality assurance

Author: Thavarshan

TESTING.md

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+# PHPVM GitHub Actions Testing Suite
+
+## Overview
+
+This document describes the comprehensive GitHub Actions testing suite set up for phpvm to ensure reliable functionality across multiple platforms and environments.
+
+## Workflows Created
+
+### 1. **Comprehensive Test** (`comprehensive-test.yml`)
+**Purpose**: Main testing workflow covering all core functionality
+**Triggers**: Push to main/development/fix/feature branches, PRs, weekly schedule
+**Platforms**: Ubuntu (latest, 20.04), macOS (latest, 12)
+
+**Test Coverage**:
+- ✅ Syntax validation and ShellCheck analysis
+- ✅ All version commands (`phpvm version`, `phpvm --version`, `phpvm -v`) 
+- ✅ Help and list commands
+- ✅ Integrated self-tests
+- ✅ PHP installation and version switching
+- ✅ System PHP switching with improved messaging
+- ✅ `.phpvmrc` auto-switching functionality
+- ✅ Error handling for invalid commands/versions
+- ✅ Cross-platform compatibility (macOS Homebrew + Linux package managers)
+- ✅ Shell compatibility testing (bash, zsh)
+- ✅ Performance benchmarking and memory usage
+
+### 2. **Edge Cases** (`edge-cases.yml`)
+**Purpose**: Test edge cases and cross-platform compatibility issues
+**Triggers**: Push to main, PRs, manual dispatch
+
+**Test Coverage**:
+- ✅ WSL simulation and bash-specific features
+- ✅ Multiple Linux distribution containers (Ubuntu, Debian, CentOS)
+- ✅ Package manager detection across different systems
+- ✅ Version command consistency verification
+- ✅ Enhanced error handling validation
+- ✅ Homebrew integration edge cases on macOS
+- ✅ `.phpvmrc` edge cases (missing, empty, invalid, whitespace)
+- ✅ Self-test robustness across multiple runs
+- ✅ Resource usage monitoring
+
+### 3. **Installation Testing** (`installation-test.yml`)
+**Purpose**: Verify installation processes and scripts
+**Triggers**: Push to main, PRs, manual dispatch, releases
+
+**Test Coverage**:
+- ✅ Installation script syntax validation
+- ✅ cURL-based installation testing
+- ✅ Installation verification and functionality checks
+- ✅ Uninstallation process testing
+- ✅ Cross-platform installation compatibility
+
+### 4. **Release Testing** (`release-test.yml`)
+**Purpose**: Final verification for releases
+**Triggers**: Published releases, pre-releases, manual dispatch
+
+**Test Coverage**:
+- ✅ Release version verification
+- ✅ All core commands functionality
+- ✅ Installation from release tags
+- ✅ Performance regression testing
+- ✅ Documentation verification (README, commands)
+- ✅ Changelog verification
+
+### 5. **Existing Workflows** (Enhanced)
+- `test.yml`: Basic integrated self-tests
+- `use.yml`: PHP installation and usage workflow
+
+## Key Testing Features
+
+### **v1.5.0 Specific Testing**
+- ✅ **New Version Commands**: All three variants (`version`, `--version`, `-v`)
+- ✅ **Enhanced Cross-Platform Support**: WSL, Linux distributions
+- ✅ **Improved Error Handling**: Homebrew link failures, missing binaries
+- ✅ **System PHP Messaging**: Updated "Homebrew default PHP" messaging
+- ✅ **Bash Shebang Compatibility**: WSL and Linux shell compatibility
+- ✅ **Post-Install Validation**: Binary availability checks
+
+### **Platform Coverage**
+- **macOS**: Latest and macOS-12 with Homebrew integration
+- **Ubuntu**: Latest and 20.04 LTS versions
+- **Linux Containers**: Debian, CentOS for broad compatibility
+- **Package Managers**: brew, apt, dnf, yum, pacman detection
+- **Shell Environments**: bash, zsh, dash (POSIX) compatibility
+
+### **Test Categories**
+1. **Functional Tests**: All commands work as expected
+2. **Integration Tests**: Installation, switching, auto-switching
+3. **Compatibility Tests**: Cross-platform, shell, distribution
+4. **Edge Case Tests**: Error conditions, malformed inputs
+5. **Performance Tests**: Speed, memory usage, regression
+6. **Installation Tests**: cURL, wget, verification, cleanup
+
+## Workflow Execution
+
+### **Automatic Triggers**
+- **Push** to main, development, fix/*, feature/* branches
+- **Pull Requests** to main, development
+- **Releases** (published, pre-released)
+- **Scheduled** (weekly on Sundays at 2 AM UTC)
+
+### **Manual Triggers**
+- All workflows support `workflow_dispatch` for manual execution
+- Release testing can be triggered with custom version input
+
+## Benefits
+
+### **Quality Assurance**
+- ✅ **Multi-Platform Validation**: Ensures phpvm works on all supported systems
+- ✅ **Regression Prevention**: Catches issues before they reach users
+- ✅ **Edge Case Coverage**: Tests unusual scenarios and error conditions
+- ✅ **Performance Monitoring**: Tracks resource usage and execution speed
+
+### **Development Confidence**
+- ✅ **Automated Validation**: Every change is thoroughly tested
+- ✅ **Cross-Platform Verification**: No platform-specific issues slip through
+- ✅ **Release Readiness**: Comprehensive validation before releases
+- ✅ **Documentation Sync**: Ensures docs match functionality
+
+### **User Experience**
+- ✅ **Reliable Installation**: Installation methods are verified to work
+- ✅ **Cross-Platform Consistency**: Same experience across all platforms
+- ✅ **Error Handling**: Users get helpful error messages
+- ✅ **Performance**: Commands execute efficiently
+
+## Maintenance
+
+### **Workflow Updates**
+- Workflows are version-controlled and can be updated with phpvm changes
+- New features should add corresponding tests to relevant workflows
+- Platform versions should be updated periodically (Ubuntu LTS, macOS versions)
+
+### **Monitoring**
+- GitHub Actions dashboard shows workflow status
+- Failed workflows require investigation and fixes
+- Performance trends can be monitored over time
+
+## Usage
+
+### **For Contributors**
+- All PRs automatically trigger comprehensive testing
+- Check workflow results before merging
+- Add new tests when adding new features
+
+### **For Maintainers**
+- Monitor workflow health and update as needed
+- Use release workflows for final verification
+- Review performance trends and address regressions
+
+### **For Users**
+- Badge status in README shows current test status
+- Release workflows ensure stable releases
+- Installation methods are continuously verified
+
+## Conclusion
+
+This comprehensive testing suite ensures phpvm v1.5.0 and future versions maintain high quality, reliability, and cross-platform compatibility. The automated workflows catch issues early, provide confidence in releases, and ensure a consistent user experience across all supported platforms.
+
+The 823 lines of workflow configuration provide extensive coverage that would be impractical to test manually, making this an essential part of the phpvm development process.