diff --git a/install.sh b/install.sh
index fcfacec..42369a2 100644
--- a/install.sh
+++ b/install.sh
@@ -1,25 +1,25 @@
-#!/usr/bin/env bash
-
-{ # Ensure the entire script is downloaded and executed
-
-    set -euo pipefail
+#!/bin/sh
+{
+    # Ensure the entire script is downloaded and executed
+    set -e
 
     phpvm_has() {
-        type "$1" >/dev/null 2>&1
+        command -v "$1" >/dev/null 2>&1
     }
 
     phpvm_echo() {
-        command printf "\e[32m%s\e[0m\n" "$*"
+        printf "\033[32m%s\033[0m\n" "$*"
     }
 
     phpvm_err() {
-        command >&2 printf "\e[31mError: %s\e[0m\n" "$*"
+        printf "\033[31mError: %s\033[0m\n" "$*" >&2
     }
 
     phpvm_warn() {
-        command >&2 printf "\e[33mWarning: %s\e[0m\n" "$*"
+        printf "\033[33mWarning: %s\033[0m\n" "$*" >&2
     }
 
+    # Default installation directory
     PHPVM_DIR="${PHPVM_DIR:-$HOME/.phpvm}"
     PHPVM_SCRIPT="$PHPVM_DIR/phpvm.sh"
     GITHUB_REPO_URL="https://raw.githubusercontent.com/Thavarshan/phpvm/main/phpvm.sh"
@@ -36,7 +36,8 @@
         if phpvm_has "curl"; then
             curl --fail --compressed -q "$@"
         elif phpvm_has "wget"; then
-            wget "$@"
+            # Adding -O- to output to stdout for wget
+            wget -O- "$@"
         else
             phpvm_err "curl or wget is required to install phpvm."
             exit 1
@@ -49,11 +50,20 @@
             return
         fi
 
-        local DETECTED_PROFILE=''
-        if [ "${SHELL#*zsh}" != "$SHELL" ]; then
-            if [ -f "$HOME/.zshrc" ]; then DETECTED_PROFILE="$HOME/.zshrc"; fi
-        elif [ "${SHELL#*bash}" != "$SHELL" ]; then
-            if [ -f "$HOME/.bashrc" ]; then DETECTED_PROFILE="$HOME/.bashrc"; fi
+        local DETECTED_PROFILE=""
+        local SHELL_NAME=""
+
+        # Get the shell from PS1 or SHELL variable
+        SHELL_NAME="$(basename "$SHELL")"
+
+        if [ "$SHELL_NAME" = "zsh" ]; then
+            if [ -f "$HOME/.zshrc" ]; then
+                DETECTED_PROFILE="$HOME/.zshrc"
+            fi
+        elif [ "$SHELL_NAME" = "bash" ]; then
+            if [ -f "$HOME/.bashrc" ]; then
+                DETECTED_PROFILE="$HOME/.bashrc"
+            fi
         fi
 
         if [ -z "$DETECTED_PROFILE" ]; then
@@ -71,10 +81,14 @@
     install_phpvm_as_script() {
         local INSTALL_DIR
         INSTALL_DIR="$(phpvm_install_dir)"
-
         mkdir -p "$INSTALL_DIR/bin"
+
         phpvm_echo "Downloading phpvm script from $GITHUB_REPO_URL..."
-        phpvm_download -fsSL "$GITHUB_REPO_URL" -o "$INSTALL_DIR/phpvm.sh"
+        phpvm_download "$GITHUB_REPO_URL" >"$INSTALL_DIR/phpvm.sh" || {
+            phpvm_err "Failed to download phpvm script"
+            exit 1
+        }
+
         chmod +x "$INSTALL_DIR/phpvm.sh"
         ln -sf "$INSTALL_DIR/phpvm.sh" "$INSTALL_DIR/bin/phpvm"
     }
@@ -86,19 +100,23 @@
         local PROFILE
         PROFILE="$(phpvm_detect_profile)"
 
-        if [ -n "$PROFILE" ] && ! grep -qc 'phpvm.sh' "$PROFILE"; then
+        if [ -n "$PROFILE" ] && ! grep -q 'phpvm.sh' "$PROFILE"; then
             phpvm_echo "Appending phpvm source to $PROFILE"
-            echo -e "\nexport PHPVM_DIR=\"$(phpvm_install_dir)\"\nexport PATH=\"\$PHPVM_DIR/bin:\$PATH\"\n[ -s \"\$PHPVM_DIR/phpvm.sh\" ] && \\. \"\$PHPVM_DIR/phpvm.sh\"" >>"$PROFILE"
+            printf "\nexport PHPVM_DIR=\"%s\"\nexport PATH=\"\$PHPVM_DIR/bin:\$PATH\"\n[ -s \"\$PHPVM_DIR/phpvm.sh\" ] && . \"\$PHPVM_DIR/phpvm.sh\"\n" "$(phpvm_install_dir)" >>"$PROFILE"
         fi
 
         phpvm_echo "Applying changes..."
         export PATH="$PHPVM_DIR/bin:$PATH"
-        source "$PROFILE" || true
+
+        # Only source the profile if it exists
+        if [ -f "$PROFILE" ]; then
+            # Use . instead of source for POSIX compatibility
+            . "$PROFILE" || true
+        fi
 
         phpvm_echo "phpvm installation complete!"
         phpvm_echo "Run: phpvm use 8.4"
     }
 
     phpvm_do_install
-
 } # End of script
diff --git a/phpvm.sh b/phpvm.sh
index 9faf8c0..12d855f 100755
--- a/phpvm.sh
+++ b/phpvm.sh
@@ -1,19 +1,19 @@
 #!/bin/sh
 
-# phpvm - A PHP Version Manager written in Shell
+# phpvm - A PHP Version Manager for macOS and Linux
 
 PHPVM_DIR="$HOME/.phpvm"
 PHPVM_VERSIONS_DIR="$PHPVM_DIR/versions"
 PHPVM_ACTIVE_VERSION_FILE="$PHPVM_DIR/active_version"
 PHPVM_CURRENT_SYMLINK="$PHPVM_DIR/current"
-HOMEBREW_PHP_CELLAR="/opt/homebrew/Cellar"
-HOMEBREW_PHP_BIN="/opt/homebrew/bin"
 DEBUG=false # Set to true to enable debug logs
 
-# Create the required directory and exit if it fails.
-mkdir -p "$PHPVM_VERSIONS_DIR" || {
-    echo "Error: Failed to create directory $PHPVM_VERSIONS_DIR" >&2
-    exit 1
+# Create the required directory structure
+create_directories() {
+    mkdir -p "$PHPVM_VERSIONS_DIR" || {
+        echo "Error: Failed to create directory $PHPVM_VERSIONS_DIR" >&2
+        exit 1
+    }
 }
 
 # ANSI color codes
@@ -28,102 +28,212 @@ phpvm_err() { printf "%sError: %s%s\n" "$RED" "$*" "$RESET" >&2; }
 phpvm_warn() { printf "%sWarning: %s%s\n" "$YELLOW" "$*" "$RESET" >&2; }
 phpvm_debug() { [ "$DEBUG" = "true" ] && echo "Debug: $*"; }
 
-# Helper function to check if Homebrew is installed
-is_brew_installed() {
-    command -v brew >/dev/null 2>&1
-}
-
-# Ensure Homebrew is installed before proceeding
-if ! is_brew_installed; then
-    phpvm_err "Homebrew is not installed. Please install Homebrew first."
-    exit 1
-fi
-
-# Helper function to install PHP using Homebrew
-brew_install_php() {
-    version="$1"
-    phpvm_debug "Attempting to install PHP $version using Homebrew..."
-    if ! brew install php@"$version"; then
-        phpvm_warn "php@$version is not available in Homebrew. Trying latest version..."
-        if ! brew install php; then
-            phpvm_err "Failed to install PHP."
-            return 1
+# Detect the system's package manager and OS
+detect_system() {
+    if [ "$(uname)" = "Darwin" ]; then
+        PKG_MANAGER="brew"
+        if ! command -v brew >/dev/null 2>&1; then
+            phpvm_err "Homebrew is not installed. Please install Homebrew first."
+            exit 1
         fi
+        HOMEBREW_PREFIX="/opt/homebrew"
+        PHP_BIN_PATH="$HOMEBREW_PREFIX/bin"
+        return 0
     fi
-    return 0
-}
 
-# Helper function to get the installed PHP version
-get_installed_php_version() {
-    phpvm_debug "Getting installed PHP version..."
-    if command -v php-config >/dev/null 2>&1; then
-        php-config --version
+    # Detect Linux package manager
+    if command -v apt-get >/dev/null 2>&1; then
+        PKG_MANAGER="apt"
+        PHP_BIN_PATH="/usr/bin"
+    elif command -v dnf >/dev/null 2>&1; then
+        PKG_MANAGER="dnf"
+        PHP_BIN_PATH="/usr/bin"
+    elif command -v yum >/dev/null 2>&1; then
+        PKG_MANAGER="yum"
+        PHP_BIN_PATH="/usr/bin"
+    elif command -v pacman >/dev/null 2>&1; then
+        PKG_MANAGER="pacman"
+        PHP_BIN_PATH="/usr/bin"
+    elif command -v brew >/dev/null 2>&1; then
+        PKG_MANAGER="brew"
+        # Detect Linuxbrew path
+        if [ -d "/home/linuxbrew/.linuxbrew" ]; then
+            HOMEBREW_PREFIX="/home/linuxbrew/.linuxbrew"
+        elif [ -d "$HOME/.linuxbrew" ]; then
+            HOMEBREW_PREFIX="$HOME/.linuxbrew"
+        else
+            HOMEBREW_PREFIX="/usr/local" # Fallback location
+        fi
+        PHP_BIN_PATH="$HOMEBREW_PREFIX/bin"
     else
-        php -v | awk '/^PHP/ {print $2}'
+        phpvm_err "No supported package manager found (apt, dnf, yum, pacman, or brew)."
+        exit 1
     fi
 }
 
+# Install PHP using the detected package manager
 install_php() {
     version="$1"
     [ -z "$version" ] && {
         phpvm_err "No PHP version specified for installation."
         return 1
     }
+
     phpvm_echo "Installing PHP $version..."
-    brew_install_php "$version" || return 1
+
+    case "$PKG_MANAGER" in
+    brew)
+        if ! brew install php@"$version"; then
+            phpvm_warn "php@$version is not available in Homebrew. Trying latest version..."
+            if ! brew install php; then
+                phpvm_err "Failed to install PHP."
+                return 1
+            fi
+        fi
+        ;;
+    apt)
+        # Check if we need sudo
+        if [ "$(id -u)" -ne 0 ]; then
+            SUDO="sudo"
+        else
+            SUDO=""
+        fi
+
+        $SUDO apt-get update
+        if ! $SUDO apt-get install -y php"$version"; then
+            phpvm_err "Failed to install PHP $version. Package php$version may not exist."
+            return 1
+        fi
+        ;;
+    dnf | yum)
+        # Check if we need sudo
+        if [ "$(id -u)" -ne 0 ]; then
+            SUDO="sudo"
+        else
+            SUDO=""
+        fi
+
+        if ! $SUDO $PKG_MANAGER install -y php"$version"; then
+            # Try with full version format for some repos
+            if ! $SUDO $PKG_MANAGER install -y php-"$version".0; then
+                phpvm_err "Failed to install PHP $version. Package php$version may not exist."
+                return 1
+            fi
+        fi
+        ;;
+    pacman)
+        # Check if we need sudo
+        if [ "$(id -u)" -ne 0 ]; then
+            SUDO="sudo"
+        else
+            SUDO=""
+        fi
+
+        $SUDO pacman -Sy
+        if ! $SUDO pacman -S --noconfirm php"$version"; then
+            phpvm_err "Failed to install PHP $version. Package php$version may not exist."
+            return 1
+        fi
+        ;;
+    esac
+
     phpvm_echo "PHP $version installed."
     return 0
 }
 
+# Helper function to get the installed PHP version
+get_installed_php_version() {
+    phpvm_debug "Getting installed PHP version..."
+    if command -v php-config >/dev/null 2>&1; then
+        php-config --version
+    else
+        php -v | awk '/^PHP/ {print $2}'
+    fi
+}
+
 use_php_version() {
     version="$1"
     [ -z "$version" ] && {
         phpvm_err "No PHP version specified to switch."
         return 1
     }
+
     phpvm_echo "Switching to PHP $version..."
-    phpvm_debug "Unlinking any existing PHP version..."
-    brew unlink php >/dev/null 2>&1 || phpvm_warn "Failed to unlink current PHP version."
-    if [ -d "$HOMEBREW_PHP_CELLAR/php@$version" ]; then
-        phpvm_debug "Linking PHP $version..."
-        brew link php@"$version" --force --overwrite || {
-            phpvm_err "Failed to link PHP $version."
+
+    case "$PKG_MANAGER" in
+    brew)
+        phpvm_debug "Unlinking any existing PHP version..."
+        brew unlink php >/dev/null 2>&1 || phpvm_warn "Failed to unlink current PHP version."
+
+        if [ -d "$HOMEBREW_PREFIX/Cellar/php@$version" ]; then
+            phpvm_debug "Linking PHP $version..."
+            brew link php@"$version" --force --overwrite || {
+                phpvm_err "Failed to link PHP $version."
+                return 1
+            }
+        elif [ -d "$HOMEBREW_PREFIX/Cellar/php" ]; then
+            installed_version=$(get_installed_php_version)
+            if [ "$installed_version" = "$version" ]; then
+                phpvm_echo "Using PHP $version installed as 'php'."
+            else
+                phpvm_err "PHP version $version is not installed. Installed version: $installed_version"
+                return 1
+            fi
+        else
+            phpvm_err "PHP version $version is not installed."
             return 1
-        }
-    elif [ -d "$HOMEBREW_PHP_CELLAR/php" ]; then
-        installed_version=$(get_installed_php_version)
-        if [ "$installed_version" = "$version" ]; then
-            phpvm_echo "Using PHP $version installed as 'php'."
+        fi
+        ;;
+    apt | dnf | yum | pacman)
+        # For Linux package managers, we use update-alternatives if available
+        if command -v update-alternatives >/dev/null 2>&1; then
+            # Check if we need sudo
+            if [ "$(id -u)" -ne 0 ]; then
+                SUDO="sudo"
+            else
+                SUDO=""
+            fi
+
+            if [ -f "/usr/bin/php$version" ]; then
+                $SUDO update-alternatives --set php "/usr/bin/php$version" || {
+                    phpvm_err "Failed to switch to PHP $version using update-alternatives."
+                    return 1
+                }
+            else
+                phpvm_err "PHP binary for version $version not found at /usr/bin/php$version"
+                return 1
+            fi
         else
-            phpvm_err "PHP version $version is not installed. Installed version: $installed_version"
+            phpvm_err "update-alternatives command not found. Cannot switch PHP versions on this system."
             return 1
         fi
-    else
-        phpvm_err "PHP version $version is not installed."
-        return 1
-    }
+        ;;
+    esac
+
     phpvm_debug "Updating symlink to PHP $version..."
     rm -f "$PHPVM_CURRENT_SYMLINK"
-    ln -s "$HOMEBREW_PHP_BIN/php" "$PHPVM_CURRENT_SYMLINK" || {
+    ln -s "$PHP_BIN_PATH/php" "$PHPVM_CURRENT_SYMLINK" || {
         phpvm_err "Failed to update symlink."
         return 1
     }
+
     echo "$version" >"$PHPVM_ACTIVE_VERSION_FILE" || {
         phpvm_err "Failed to write active version."
         return 1
     }
+
     phpvm_echo "Switched to PHP $version."
+    return 0
 }
 
 auto_switch_php_version() {
-    local current_dir="$PWD"
-    local found=0
-    local depth=0
-    local max_depth=5
+    current_dir="$PWD"
+    found=0
+    depth=0
+    max_depth=5
 
     while [ "$current_dir" != "/" ] && [ $depth -lt $max_depth ]; do
         if [ -f "$current_dir/.phpvmrc" ]; then
-            local version
             if ! version=$(tr -d '[:space:]' <"$current_dir/.phpvmrc"); then
                 phpvm_err "Failed to read $current_dir/.phpvmrc"
                 return 1
@@ -152,34 +262,106 @@ auto_switch_php_version() {
     return 0
 }
 
+list_installed_versions() {
+    phpvm_echo "Installed PHP versions:"
+
+    case "$PKG_MANAGER" in
+    brew)
+        if [ -d "$HOMEBREW_PREFIX/Cellar" ]; then
+            for dir in "$HOMEBREW_PREFIX/Cellar/php"*; do
+                if [ -d "$dir" ]; then
+                    base_name=$(basename "$dir")
+                    if [ "$base_name" = "php" ]; then
+                        version=$(get_installed_php_version)
+                        echo "  $version (latest)"
+                    else
+                        # Extract version from php@X.Y format
+                        version=${base_name#php@}
+                        echo "  $version"
+                    fi
+                fi
+            done
+        fi
+        ;;
+    apt)
+        dpkg -l | grep -E '^ii +php[0-9]+\.[0-9]+' | awk '{print "  " $2}' | sed 's/^  php//'
+        ;;
+    dnf | yum)
+        $PKG_MANAGER list installed | grep -E 'php[0-9]+\.' | awk '{print "  " $1}' | sed 's/^  php//'
+        ;;
+    pacman)
+        pacman -Q | grep '^php' | awk '{print "  " $1}' | sed 's/^  php//'
+        ;;
+    esac
+
+    echo ""
+    if [ -f "$PHPVM_ACTIVE_VERSION_FILE" ]; then
+        active_version=$(cat "$PHPVM_ACTIVE_VERSION_FILE")
+        phpvm_echo "Active version: $active_version"
+    else
+        phpvm_warn "No active PHP version set."
+    fi
+}
+
+print_help() {
+    cat <<EOF
+phpvm - PHP Version Manager
+
+Usage:
+  phpvm install <version>  Install specified PHP version
+  phpvm use <version>      Switch to specified PHP version
+  phpvm auto               Auto-switch based on .phpvmrc file
+  phpvm list               List installed PHP versions
+  phpvm help               Show this help message
+
+Examples:
+  phpvm install 8.1        Install PHP 8.1
+  phpvm use 7.4            Switch to PHP 7.4
+  phpvm auto               Auto-switch based on current directory
+EOF
+}
+
 main() {
+    create_directories
+    detect_system
+
     if [ "$#" -eq 0 ]; then
-        phpvm_err "No command provided. Available commands: install <version>, use <version>."
-        return 1
+        phpvm_err "No command provided."
+        print_help
+        exit 1
     fi
+
     command="$1"
     shift
+
     case "$command" in
     use)
         if [ "$#" -eq 0 ]; then
             phpvm_err "Missing PHP version argument for 'use' command."
-            return 1
+            exit 1
         fi
         use_php_version "$@"
         ;;
     install)
         if [ "$#" -eq 0 ]; then
             phpvm_err "Missing PHP version argument for 'install' command."
-            return 1
+            exit 1
         fi
         install_php "$@"
         ;;
     auto)
         auto_switch_php_version
         ;;
+    list)
+        list_installed_versions
+        ;;
+    help)
+        print_help
+        ;;
     *)
-        phpvm_err "Unknown command: $command. Available commands: install <version>, use <version>."
-        return 1
+        phpvm_err "Unknown command: $command"
+        print_help
+        exit 1
         ;;
     esac
 }
diff --git a/test_phpvm.bats b/test_phpvm.bats
index ef3f884..ba889d1 100644
--- a/test_phpvm.bats
+++ b/test_phpvm.bats
@@ -1,68 +1,209 @@
 #!/usr/bin/env bats
 
-# Source the script under test.
+# Set up test environment
 setup() {
-  ORIGINAL_PATH="$PATH"
-  MOCK_DIR="$(mktemp -d)"
-  PATH="$MOCK_DIR:$PATH"
+  # Create a temporary directory for tests
+  export TEMP_DIR=$(mktemp -d)
+  export HOME="$TEMP_DIR"
+  export PHPVM_DIR="$HOME/.phpvm"
+  export PHPVM_VERSIONS_DIR="$PHPVM_DIR/versions"
+  export PHPVM_ACTIVE_VERSION_FILE="$PHPVM_DIR/active_version"
+  export PHPVM_CURRENT_SYMLINK="$PHPVM_DIR/current"
 
-  # Ensure phpvm.sh exists before sourcing
-  if [[ ! -f "./phpvm.sh" ]]; then
-    echo "Error: phpvm.sh not found!"
-    exit 1
-  fi
+  # Mock the brew command
+  mkdir -p "$TEMP_DIR/bin"
+  cat >"$TEMP_DIR/bin/brew" <<'EOF'
+#!/bin/sh
+if [ "$1" = "install" ]; then
+    if [ "$2" = "php@7.4" ]; then
+        echo "Installing php@7.4..."
+        mkdir -p /opt/homebrew/Cellar/php@7.4/bin
+        return 0
+    elif [ "$2" = "php" ]; then
+        echo "Installing php (latest)..."
+        mkdir -p /opt/homebrew/Cellar/php/bin
+        return 0
+    else
+        echo "Error: Formula php@$2 not available" >&2
+        return 1
+    fi
+elif [ "$1" = "unlink" ]; then
+    return 0
+elif [ "$1" = "link" ]; then
+    return 0
+fi
+EOF
+  chmod +x "$TEMP_DIR/bin/brew"
 
-  chmod +x "./phpvm.sh"
-  source "./phpvm.sh"
+  # Mock php and php-config
+  cat >"$TEMP_DIR/bin/php" <<'EOF'
+#!/bin/sh
+if [ "$1" = "-v" ]; then
+    echo "PHP 8.0.0 (cli)"
+fi
+EOF
+  chmod +x "$TEMP_DIR/bin/php"
+
+  cat >"$TEMP_DIR/bin/php-config" <<'EOF'
+#!/bin/sh
+if [ "$1" = "--version" ]; then
+    echo "8.0.0"
+fi
+EOF
+  chmod +x "$TEMP_DIR/bin/php-config"
+
+  # Add mocks to PATH
+  export PATH="$TEMP_DIR/bin:$PATH"
+
+  # Create required directories
+  mkdir -p /opt/homebrew/Cellar
+  mkdir -p /opt/homebrew/bin
+
+  # Source the script under test
+  source ./phpvm
 }
 
+# Clean up after tests
 teardown() {
-  PATH="$ORIGINAL_PATH"
-  rm -rf "$MOCK_DIR"
-  # Ensure .phpvmrc exists before attempting to remove it
-  if [[ -f "$PWD/.phpvmrc" ]]; then
-    rm -f "$PWD/.phpvmrc"
-  fi
+  rm -rf "$TEMP_DIR"
+}
+
+# Utility function to create mock PHP installations
+create_mock_php_installation() {
+  local version="$1"
+  mkdir -p "/opt/homebrew/Cellar/php@$version"
+  mkdir -p "/opt/homebrew/bin"
+  touch "/opt/homebrew/bin/php"
+}
+
+# Test directory creation
+@test "phpvm creates required directories" {
+  rm -rf "$PHPVM_DIR"
+  mkdir -p "$PHPVM_DIR" || true
+  [ -d "$PHPVM_VERSIONS_DIR" ]
+}
+
+# Test install command
+@test "install command with valid version" {
+  run install_php "7.4"
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"Installing PHP 7.4"* ]]
+  [[ "$output" == *"PHP 7.4 installed"* ]]
 }
 
-@test "install_php returns error if version not provided" {
+@test "install command with missing version" {
   run install_php ""
-  [ "$status" -ne 0 ]
-  [[ "$output" == *"No PHP version specified"* ]]
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"No PHP version specified for installation"* ]]
 }
 
-@test "install_php calls brew with version" {
-  run install_php "8.3"
+# Test use command
+@test "use command with installed version" {
+  create_mock_php_installation "7.4"
+  run use_php_version "7.4"
   [ "$status" -eq 0 ]
-  [[ "$output" == *"Installing PHP 8.3..."* ]]
-  [[ "$output" == *"PHP 8.3 installed."* ]]
+  [[ "$output" == *"Switching to PHP 7.4"* ]]
+  [[ "$output" == *"Switched to PHP 7.4"* ]]
+  [ "$(cat $PHPVM_ACTIVE_VERSION_FILE)" == "7.4" ]
 }
 
-@test "use_php_version returns error if version not provided" {
+@test "use command with missing version" {
   run use_php_version ""
-  [ "$status" -ne 0 ]
-  [[ "$output" == *"No PHP version specified to switch."* ]]
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"No PHP version specified to switch"* ]]
 }
 
-@test "use_php_version returns error if version not installed (brew cellar missing)" {
-  run use_php_version "7.4"
-  [ "$status" -ne 0 ]
-  [[ "$output" == *"PHP version 7.4 is not installed"* ]]
+@test "use command with non-installed version" {
+  run use_php_version "5.6"
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"PHP version 5.6 is not installed"* ]]
 }
 
-@test "auto_switch_php_version warns when .phpvmrc is not found" {
+# Test auto-switch functionality
+@test "auto-switch with valid .phpvmrc" {
+  create_mock_php_installation "7.4"
+  mkdir -p "$HOME/project"
+  echo "7.4" >"$HOME/project/.phpvmrc"
+  cd "$HOME/project"
   run auto_switch_php_version
-  [ "$status" -ne 0 ]
-  [[ "$output" == *"No .phpvmrc file found"* ]]
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"Auto-switching to PHP 7.4"* ]]
+  [ "$(cat $PHPVM_ACTIVE_VERSION_FILE)" == "7.4" ]
+}
+
+@test "auto-switch with invalid .phpvmrc" {
+  mkdir -p "$HOME/project"
+  echo "" >"$HOME/project/.phpvmrc"
+  cd "$HOME/project"
+  run auto_switch_php_version
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"No valid PHP version found"* ]]
 }
 
-@test "auto_switch_php_version switches PHP version from .phpvmrc" {
-  echo "8.3" >.phpvmrc
-  export HOMEBREW_PHP_CELLAR="/opt/homebrew/Cellar"
-  export HOMEBREW_PHP_BIN="/opt/homebrew/bin" # Ensure binary path is available
+@test "auto-switch with no .phpvmrc" {
+  mkdir -p "$HOME/project"
+  cd "$HOME/project"
   run auto_switch_php_version
-  echo "Test output: $output" # Debugging line to inspect output
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"No .phpvmrc file found"* ]]
+}
+
+# Test main command dispatcher
+@test "main with no arguments" {
+  run main
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"No command provided"* ]]
+}
+
+@test "main with unknown command" {
+  run main "unknown"
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"Unknown command: unknown"* ]]
+}
+
+@test "main with use command but no version" {
+  run main "use"
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"Missing PHP version argument for 'use' command"* ]]
+}
+
+@test "main with install command but no version" {
+  run main "install"
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"Missing PHP version argument for 'install' command"* ]]
+}
+
+@test "main with valid use command" {
+  create_mock_php_installation "7.4"
+  run main "use" "7.4"
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"Switched to PHP 7.4"* ]]
+}
+
+@test "main with valid install command" {
+  run main "install" "7.4"
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"PHP 7.4 installed"* ]]
+}
+
+@test "main with valid auto command" {
+  create_mock_php_installation "7.4"
+  mkdir -p "$HOME/project"
+  echo "7.4" >"$HOME/project/.phpvmrc"
+  cd "$HOME/project"
+  run main "auto"
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"Auto-switching to PHP 7.4"* ]]
+}
+
+# Test helper functions
+@test "get_installed_php_version returns correct version" {
+  run get_installed_php_version
+  [ "$status" -eq 0 ]
+  [ "$output" = "8.0.0" ]
+}
+
+@test "is_brew_installed returns success" {
+  run is_brew_installed
   [ "$status" -eq 0 ]
-  [[ "$output" == *"Auto-switching to PHP 8.3"* ]]
-  rm -f .phpvmrc # Cleanup after test
 }