diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..06bf713
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,24 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Run ShellCheck
+        run: find . -name '*.sh' -not -path './zsh/*' -print0 | xargs -0 shellcheck
+
+  test:
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install bats-core
+        run: brew install bats-core
+      - name: Run tests
+        run: bats test_install.bats
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..b908d4c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+__pycache__/
+*.pyc
+.DS_Store
diff --git a/install.sh b/install.sh
index a64853b..a8ae931 100755
--- a/install.sh
+++ b/install.sh
@@ -3,6 +3,7 @@
 set -euo pipefail
 
 REPO_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+DRY_RUN=false
 
 # ---------------------------------------------------------------------------
 # Helpers
@@ -11,6 +12,11 @@ REPO_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 _symlink() {
     local source="$1" destination="$2"
 
+    if $DRY_RUN; then
+        echo "DRY-RUN: Would link $source -> $destination"
+        return
+    fi
+
     # Already linked correctly — nothing to do
     if [ -L "$destination" ] && [ "$(readlink "$destination")" = "$source" ]; then
         echo "INFO: Nothing to do here: $destination LGTM."
@@ -19,8 +25,10 @@ _symlink() {
 
     # Back up existing file/symlink
     if [ -e "$destination" ] || [ -L "$destination" ]; then
-        mv "$destination" "${destination}.orig"
-        echo "INFO: Created backup ${destination}.orig"
+        local backup
+        backup="${destination}.orig.$(date +%Y%m%d%H%M%S)"
+        mv "$destination" "$backup"
+        echo "INFO: Created backup $backup"
     fi
 
     ln -s "$source" "$destination"
@@ -38,6 +46,7 @@ Options:
   --osx         Run macOS system tweaks (osx/osx.sh)
   --oh-my-zsh   Install Oh-my-zsh
   --claude      Link Claude Code skills to ~/.claude/skills/
+  --dry-run     Preview what would be done without making changes
   --help        Show this help message
 EOF
 }
@@ -67,6 +76,10 @@ do_ghostty() {
 
 do_brew() {
     echo "Working on Brew and programs.."
+    if $DRY_RUN; then
+        echo "DRY-RUN: Would install Xcode CLI tools, Homebrew, and packages from Brewfile"
+        return
+    fi
     if ! xcode-select -p &>/dev/null; then
         xcode-select --install
     fi
@@ -78,11 +91,23 @@ do_brew() {
 
 do_osx() {
     echo "Working on osx customisations.."
+    if $DRY_RUN; then
+        echo "DRY-RUN: Would run macOS system tweaks from osx/osx.sh"
+        return
+    fi
     bash "$REPO_DIR/osx/osx.sh"
 }
 
 do_oh_my_zsh() {
     echo "Working on Oh-my-zsh.."
+    if [ -d "$HOME/.oh-my-zsh" ]; then
+        echo "INFO: Oh-my-zsh is already installed, skipping."
+        return
+    fi
+    if $DRY_RUN; then
+        echo "DRY-RUN: Would install Oh-my-zsh"
+        return
+    fi
     curl -L https://raw.github.com/robbyrussell/oh-my-zsh/master/tools/install.sh | sh
 }
 
@@ -108,6 +133,7 @@ if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
 
     for arg in "$@"; do
         case "$arg" in
+            --dry-run)   DRY_RUN=true ;;
             --dotfiles)  do_dotfiles ;;
             --ghostty)   do_ghostty ;;
             --brew)      do_brew ;;
diff --git a/osx/osx.sh b/osx/osx.sh
index e83d9e9..c6cc899 100644
--- a/osx/osx.sh
+++ b/osx/osx.sh
@@ -1,7 +1,5 @@
 #!/usr/bin/env bash
 
-set -x
-
 #From https://mths.be/osx
 
 # Ask for the administrator password upfront
@@ -420,31 +418,12 @@ defaults write com.google.Chrome.canary AppleEnableMouseSwipeNavigateWithScrolls
 defaults write com.google.Chrome DisablePrintPreview -bool true
 defaults write com.google.Chrome.canary DisablePrintPreview -bool true
 
-###############################################################################
-# Transmission.app                                                            #
-###############################################################################
-
-# Use `~/Documents/Torrents` to store incomplete downloads
-defaults write org.m0k.transmission UseIncompleteDownloadFolder -bool true
-defaults write org.m0k.transmission IncompleteDownloadFolder -string "${HOME}/Documents/Torrents"
-
-# Don’t prompt for confirmation before downloading
-defaults write org.m0k.transmission DownloadAsk -bool false
-
-# Trash original torrent files
-defaults write org.m0k.transmission DeleteOriginalTorrent -bool true
-
-# Hide the donate message
-defaults write org.m0k.transmission WarningDonate -bool false
-# Hide the legal disclaimer
-defaults write org.m0k.transmission WarningLegal -bool false
-
 ###############################################################################
 # Kill affected applications                                                  #
 ###############################################################################
 
 for app in "Activity Monitor" "cfprefsd" "Dock" "Finder" "Messages" \
-	"SystemUIServer" "Terminal" "Transmission" "Calendar"; do
+	"SystemUIServer" "Terminal" "Calendar"; do
 	killall "${app}" > /dev/null 2>&1
 done
 echo "Done. Note that some of these changes require a logout/restart to take effect."
diff --git a/test_install.bats b/test_install.bats
index 487ec01..24a5e22 100644
--- a/test_install.bats
+++ b/test_install.bats
@@ -42,8 +42,10 @@ setup() {
 
     [ -L "$dest" ]
     [ "$(readlink "$dest")" = "$src" ]
-    [ -f "${dest}.orig" ]
-    [ "$(cat "${dest}.orig")" = "old" ]
+    local backup
+    backup=$(ls "${dest}".orig.* 2>/dev/null)
+    [ -f "$backup" ]
+    [ "$(cat "$backup")" = "old" ]
 }
 
 @test "_symlink backs up existing wrong symlink and creates correct one" {
@@ -58,8 +60,10 @@ setup() {
 
     [ -L "$dest" ]
     [ "$(readlink "$dest")" = "$src" ]
-    [ -L "${dest}.orig" ]
-    [ "$(readlink "${dest}.orig")" = "$wrong" ]
+    local backup
+    backup=$(ls "${dest}".orig.* 2>/dev/null)
+    [ -L "$backup" ]
+    [ "$(readlink "$backup")" = "$wrong" ]
 }
 
 # --- do_dotfiles test (ported from TestProccessDotfiles) ---
@@ -86,7 +90,7 @@ setup() {
 
 # --- backup test (ported from TestBackup) ---
 
-@test "backup via _symlink renames file with .orig suffix" {
+@test "backup via _symlink renames file with .orig timestamp suffix" {
     local dest="$TEST_DIR/myfile"
     local src="$TEST_DIR/newsrc"
     echo "content" > "$dest"
@@ -95,6 +99,113 @@ setup() {
     _symlink "$src" "$dest"
 
     [ -L "$dest" ]
-    [ -f "${dest}.orig" ]
-    [ "$(cat "${dest}.orig")" = "content" ]
+    local backup
+    backup=$(ls "${dest}".orig.* 2>/dev/null)
+    [ -f "$backup" ]
+    [ "$(cat "$backup")" = "content" ]
+}
+
+# --- do_ghostty tests ---
+
+@test "do_ghostty creates config directory and symlinks config" {
+    local fake_home="$TEST_DIR/home"
+    mkdir -p "$fake_home"
+
+    HOME="$fake_home"
+
+    do_ghostty
+
+    [ -d "$fake_home/.config/ghostty" ]
+    [ -L "$fake_home/.config/ghostty/config" ]
+}
+
+@test "do_ghostty is idempotent" {
+    local fake_home="$TEST_DIR/home"
+    mkdir -p "$fake_home"
+
+    HOME="$fake_home"
+
+    do_ghostty
+    run do_ghostty
+
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"LGTM"* ]]
+}
+
+# --- do_claude tests ---
+
+@test "do_claude symlinks skill directories" {
+    local fake_home="$TEST_DIR/home"
+    local repo="$TEST_DIR/repo"
+    mkdir -p "$fake_home" "$repo/claude/skills/my-skill"
+    echo "skill" > "$repo/claude/skills/my-skill/SKILL.md"
+
+    HOME="$fake_home"
+    REPO_DIR="$repo"
+
+    do_claude
+
+    [ -d "$fake_home/.claude/skills" ]
+    [ -L "$fake_home/.claude/skills/my-skill" ]
+}
+
+@test "do_claude is idempotent" {
+    local fake_home="$TEST_DIR/home"
+    local repo="$TEST_DIR/repo"
+    mkdir -p "$fake_home" "$repo/claude/skills/my-skill"
+    echo "skill" > "$repo/claude/skills/my-skill/SKILL.md"
+
+    HOME="$fake_home"
+    REPO_DIR="$repo"
+
+    do_claude
+    run do_claude
+
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"LGTM"* ]]
+}
+
+# --- do_oh_my_zsh tests ---
+
+@test "do_oh_my_zsh skips when already installed" {
+    local fake_home="$TEST_DIR/home"
+    mkdir -p "$fake_home/.oh-my-zsh"
+
+    HOME="$fake_home"
+
+    run do_oh_my_zsh
+
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"already installed"* ]]
+}
+
+# --- dry-run tests ---
+
+@test "dry-run mode prevents _symlink from creating links" {
+    local src="$TEST_DIR/source"
+    local dest="$TEST_DIR/dest"
+    echo "data" > "$src"
+
+    DRY_RUN=true
+    run _symlink "$src" "$dest"
+
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"DRY-RUN"* ]]
+    [ ! -e "$dest" ]
+}
+
+@test "dry-run mode prevents _symlink from backing up files" {
+    local src="$TEST_DIR/source"
+    local dest="$TEST_DIR/dest"
+    echo "new" > "$src"
+    echo "old" > "$dest"
+
+    DRY_RUN=true
+    run _symlink "$src" "$dest"
+
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"DRY-RUN"* ]]
+    # Original file should be untouched
+    [ -f "$dest" ]
+    [ "$(cat "$dest")" = "old" ]
 }