diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..4cf0a4e
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,42 @@
+name: Test
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+jobs:
+  test:
+    name: BATS Tests (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install bats-core (Linux)
+        if: runner.os == 'Linux'
+        run: sudo apt-get install -y bats
+
+      - name: Install bats-core (macOS)
+        if: runner.os == 'macOS'
+        run: brew install bats-core
+
+      - name: Install bats helper libraries
+        run: |
+          git clone --depth 1 https://github.com/bats-core/bats-support.git \
+            tests/test_helper/bats-support
+          git clone --depth 1 https://github.com/bats-core/bats-assert.git \
+            tests/test_helper/bats-assert
+
+      - name: Make scripts and mocks executable
+        run: |
+          chmod +x install.sh uninstall.sh shell_hook.sh post-checkout
+          chmod +x tests/test_helper/mocks/*
+
+      - name: Run tests
+        run: bats --tap tests/*.bats
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a89540b
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+# bats helper libraries (cloned at CI time, not committed)
+tests/test_helper/bats-support/
+tests/test_helper/bats-assert/
+
+.DS_Store
\ No newline at end of file
diff --git a/install.sh b/install.sh
index db01bde..fd90ff7 100755
--- a/install.sh
+++ b/install.sh
@@ -10,7 +10,7 @@
 
 TOOL_NAME="Luca"
 BIN_NAME="luca"
-INSTALL_DIR="/usr/local/bin"
+INSTALL_DIR="${INSTALL_DIR:-/usr/local/bin}"
 TOOL_FOLDER=".luca"
 VERSION_FILE="${PWD}/.luca-version"
 ORGANIZATION="LucaTools"
diff --git a/tests/fixtures/Lucafile b/tests/fixtures/Lucafile
new file mode 100644
index 0000000..bc1b62d
--- /dev/null
+++ b/tests/fixtures/Lucafile
@@ -0,0 +1,3 @@
+tools:
+  - name: mytool
+    version: "1.0.0"
diff --git a/tests/fixtures/api_response_latest.json b/tests/fixtures/api_response_latest.json
new file mode 100644
index 0000000..9fd4731
--- /dev/null
+++ b/tests/fixtures/api_response_latest.json
@@ -0,0 +1 @@
+{"tag_name": "v2.0.0", "name": "Luca v2.0.0"}
diff --git a/tests/fixtures/bashrc_with_hook b/tests/fixtures/bashrc_with_hook
new file mode 100644
index 0000000..b963410
--- /dev/null
+++ b/tests/fixtures/bashrc_with_hook
@@ -0,0 +1,4 @@
+export PATH="$PATH:/usr/local/bin"
+
+# Initialize Luca shell hook (added by Luca installer)
+[[ -s "$HOME/.luca/shell_hook.sh" ]] && source "$HOME/.luca/shell_hook.sh"
diff --git a/tests/install.bats b/tests/install.bats
new file mode 100644
index 0000000..d1720bf
--- /dev/null
+++ b/tests/install.bats
@@ -0,0 +1,230 @@
+#!/usr/bin/env bats
+
+load 'test_helper/bats-support/load'
+load 'test_helper/bats-assert/load'
+load 'test_helper/common'
+
+setup() {
+    common_setup
+}
+
+# ---------------------------------------------------------------------------
+# Version detection
+# ---------------------------------------------------------------------------
+
+@test "version: reads from .luca-version file" {
+    echo "v1.2.3" > "$BATS_TEST_TMPDIR/.luca-version"
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_output --partial "Using version from"
+    assert_output --partial "Target version: v1.2.3"
+}
+
+@test "version: fetches latest from GitHub API when no version file" {
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_output --partial "Missing"
+    assert_output --partial "Fetching the latest version"
+    assert_output --partial "v2.0.0"
+}
+
+@test "version: API returns empty object exits with error" {
+    export MOCK_CURL_BEHAVIOR=api_empty
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_failure
+    assert_output --partial "ERROR: Could not fetch latest version"
+}
+
+@test "version: invalid semver in version file exits with error" {
+    echo "not-a-version" > "$BATS_TEST_TMPDIR/.luca-version"
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_failure
+    assert_output --partial "Invalid version format"
+}
+
+@test "version: valid semver without v prefix is accepted" {
+    echo "1.2.3" > "$BATS_TEST_TMPDIR/.luca-version"
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_output --partial "Target version: 1.2.3"
+}
+
+@test "version: valid semver with prerelease tag is accepted" {
+    echo "v1.2.3-beta.1" > "$BATS_TEST_TMPDIR/.luca-version"
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_output --partial "Target version: v1.2.3-beta.1"
+}
+
+@test "version: GITHUB_TOKEN set prints authenticated request message" {
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+
+    run env GITHUB_TOKEN=mytoken bash "$REPO_ROOT/install.sh"
+
+    assert_output --partial "Using GITHUB_TOKEN for authenticated GitHub API requests"
+}
+
+# ---------------------------------------------------------------------------
+# OS detection
+# ---------------------------------------------------------------------------
+
+@test "os: Darwin detected as macOS" {
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+    # MOCK_UNAME_OUTPUT defaults to Darwin
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_output --partial "Detected macOS"
+}
+
+@test "os: Linux detected via /etc/os-release" {
+    if [ ! -f /etc/os-release ]; then
+        skip "Requires /etc/os-release (Linux only)"
+    fi
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+    export MOCK_UNAME_OUTPUT="Linux"
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_output --partial "Detected Linux"
+}
+
+# ---------------------------------------------------------------------------
+# Already up to date
+# ---------------------------------------------------------------------------
+
+@test "skip: already up-to-date version exits 0 without downloading" {
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+    export MOCK_LUCA_VERSION="v2.0.0"
+    # Place a fake luca binary that returns v2.0.0
+    cp "$TESTS_DIR/test_helper/mocks/luca" "$TEST_INSTALL_DIR/luca"
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_success
+    assert_output --partial "already up to date"
+    # Verify curl was NOT called for a download
+    refute_output --partial "Downloading"
+}
+
+@test "skip: different installed version proceeds with update" {
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+    export MOCK_LUCA_VERSION="v1.0.0"
+    cp "$TESTS_DIR/test_helper/mocks/luca" "$TEST_INSTALL_DIR/luca"
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_output --partial "Updating to version"
+}
+
+# ---------------------------------------------------------------------------
+# Download and install
+# ---------------------------------------------------------------------------
+
+@test "install: happy path installs binary to INSTALL_DIR" {
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_success
+    assert_output --partial "successfully installed"
+    assert [ -f "$TEST_INSTALL_DIR/luca" ]
+}
+
+@test "install: curl download failure exits with error" {
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+    export MOCK_CURL_BEHAVIOR=download_fail
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_failure
+    assert_output --partial "ERROR: Could not download"
+}
+
+@test "install: unzip failure exits with error and cleans up zip" {
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+    export MOCK_UNZIP_BEHAVIOR=fail
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_failure
+    assert_output --partial "ERROR: Failed to extract"
+    # Zip file should have been cleaned up
+    assert [ ! -f "$BATS_TEST_TMPDIR/Luca-macOS.zip" ]
+}
+
+# ---------------------------------------------------------------------------
+# Shell hook setup
+# ---------------------------------------------------------------------------
+
+@test "shell_hook: download failure is non-fatal (exits 0)" {
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+    export MOCK_CURL_BEHAVIOR=shell_hook_fail
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_success
+    assert_output --partial "WARNING: Could not download shell hook"
+}
+
+# ---------------------------------------------------------------------------
+# Git hook setup
+# ---------------------------------------------------------------------------
+
+@test "git: not in a git repo skips hook installation silently" {
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+    # MOCK_GIT_REPO_ROOT unset → mock git returns exit 128 (not a repo)
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_success
+    refute_output --partial "Git post-checkout hook installed"
+}
+
+@test "git: in a git repo installs post-checkout hook" {
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+    local git_root="$BATS_TEST_TMPDIR/fake_repo"
+    mkdir -p "$git_root/.git/hooks"
+    export MOCK_GIT_REPO_ROOT="$git_root"
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_success
+    assert_output --partial "Git post-checkout hook installed"
+    assert [ -f "$git_root/.git/hooks/post-checkout" ]
+}
+
+@test "git: hook with Luca identifier already exists is skipped" {
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+    local git_root="$BATS_TEST_TMPDIR/fake_repo"
+    mkdir -p "$git_root/.git/hooks"
+    echo "# LUCA POST-CHECKOUT GIT HOOK" > "$git_root/.git/hooks/post-checkout"
+    export MOCK_GIT_REPO_ROOT="$git_root"
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_success
+    assert_output --partial "Luca post-checkout hook already installed"
+}
+
+@test "git: foreign hook without Luca identifier warns and does not overwrite" {
+    echo "v2.0.0" > "$BATS_TEST_TMPDIR/.luca-version"
+    local git_root="$BATS_TEST_TMPDIR/fake_repo"
+    mkdir -p "$git_root/.git/hooks"
+    echo "#!/bin/sh\n# some other tool" > "$git_root/.git/hooks/post-checkout"
+    export MOCK_GIT_REPO_ROOT="$git_root"
+
+    run bash "$REPO_ROOT/install.sh"
+
+    assert_success
+    assert_output --partial "A post-checkout hook already exists"
+    # Original hook content should be unchanged
+    assert [ -f "$git_root/.git/hooks/post-checkout" ]
+}
diff --git a/tests/post_checkout.bats b/tests/post_checkout.bats
new file mode 100644
index 0000000..ce553ea
--- /dev/null
+++ b/tests/post_checkout.bats
@@ -0,0 +1,128 @@
+#!/usr/bin/env bats
+
+load 'test_helper/bats-support/load'
+load 'test_helper/bats-assert/load'
+load 'test_helper/common'
+
+setup() {
+    common_setup
+    # Create a fake git repo root used by most tests
+    export FAKE_REPO="$BATS_TEST_TMPDIR/repo"
+    mkdir -p "$FAKE_REPO/.git/hooks"
+    export MOCK_GIT_REPO_ROOT="$FAKE_REPO"
+    # Set up the luca call log
+    export MOCK_LUCA_CALL_LOG="$BATS_TEST_TMPDIR/luca_calls.log"
+    touch "$MOCK_LUCA_CALL_LOG"
+}
+
+# ---------------------------------------------------------------------------
+# Checkout type guard
+# ---------------------------------------------------------------------------
+
+@test "type guard: file checkout (type=0) exits 0 immediately" {
+    run "$REPO_ROOT/post-checkout" prev_ref new_ref 0
+
+    assert_success
+    assert_output ""
+}
+
+@test "type guard: missing third argument defaults to 0 and exits 0" {
+    run "$REPO_ROOT/post-checkout" prev_ref new_ref
+
+    assert_success
+    assert_output ""
+}
+
+@test "type guard: branch checkout (type=1) proceeds" {
+    # With no Lucafile, script exits 0 silently after proceeding past the guard
+    run "$REPO_ROOT/post-checkout" prev_ref new_ref 1
+
+    assert_success
+}
+
+# ---------------------------------------------------------------------------
+# Lucafile detection
+# ---------------------------------------------------------------------------
+
+@test "lucafile: no Lucafile in repo root exits 0 silently" {
+    run "$REPO_ROOT/post-checkout" prev_ref new_ref 1
+
+    assert_success
+    refute_output --partial "synchronizing"
+}
+
+@test "lucafile: Lucafile exists triggers synchronization message" {
+    cp "$FIXTURE_DIR/Lucafile" "$FAKE_REPO/Lucafile"
+
+    run "$REPO_ROOT/post-checkout" prev_ref new_ref 1
+
+    assert_success
+    assert_output --partial "Found Lucafile, synchronizing"
+}
+
+@test "lucafile: git root undetermined exits 0 with warning" {
+    unset MOCK_GIT_REPO_ROOT
+
+    run "$REPO_ROOT/post-checkout" prev_ref new_ref 1
+
+    assert_success
+    assert_output --partial "Could not determine repository root"
+}
+
+# ---------------------------------------------------------------------------
+# Luca installation check
+# ---------------------------------------------------------------------------
+
+@test "luca present: curl NOT called to install when luca already in PATH" {
+    cp "$FIXTURE_DIR/Lucafile" "$FAKE_REPO/Lucafile"
+    # luca mock is already in PATH via common_setup
+
+    run "$REPO_ROOT/post-checkout" prev_ref new_ref 1
+
+    assert_success
+    # curl should not have been invoked for install.sh
+    if [ -f "$MOCK_CALL_LOG" ]; then
+        refute grep -q "install.sh" "$MOCK_CALL_LOG" 2>/dev/null || true
+    fi
+}
+
+@test "luca absent: curl called to install when luca not in PATH" {
+    cp "$FIXTURE_DIR/Lucafile" "$FAKE_REPO/Lucafile"
+    # Build a PATH that has git/curl mocks but NOT luca
+    local no_luca_bin="$BATS_TEST_TMPDIR/no_luca_bin"
+    mkdir -p "$no_luca_bin"
+    for mock in curl git sudo uname unzip; do
+        ln -sf "$TESTS_DIR/test_helper/mocks/$mock" "$no_luca_bin/$mock"
+    done
+
+    # Intentionally omit /usr/local/bin to ensure real luca is not found
+    run env PATH="$no_luca_bin:/usr/bin:/bin" \
+        "$REPO_ROOT/post-checkout" prev_ref new_ref 1
+
+    assert_output --partial "installing"
+}
+
+# ---------------------------------------------------------------------------
+# luca install invocation
+# ---------------------------------------------------------------------------
+
+@test "luca install: called with correct args on happy path" {
+    cp "$FIXTURE_DIR/Lucafile" "$FAKE_REPO/Lucafile"
+
+    run "$REPO_ROOT/post-checkout" prev_ref new_ref 1
+
+    assert_success
+    assert_output --partial "Tools synchronized successfully"
+    run grep "luca install --quiet --spec Lucafile" "$MOCK_LUCA_CALL_LOG"
+    assert_success
+}
+
+@test "luca install: non-zero exit warns but post-checkout exits 0" {
+    cp "$FIXTURE_DIR/Lucafile" "$FAKE_REPO/Lucafile"
+    export MOCK_LUCA_INSTALL_EXIT_CODE=1
+
+    run "$REPO_ROOT/post-checkout" prev_ref new_ref 1
+
+    assert_success
+    assert_output --partial "Some tools may have failed"
+}
diff --git a/tests/shell_hook.bats b/tests/shell_hook.bats
new file mode 100644
index 0000000..8bf7a53
--- /dev/null
+++ b/tests/shell_hook.bats
@@ -0,0 +1,224 @@
+#!/usr/bin/env bats
+
+load 'test_helper/bats-support/load'
+load 'test_helper/bats-assert/load'
+load 'test_helper/common'
+
+setup() {
+    common_setup
+}
+
+# ---------------------------------------------------------------------------
+# update_path() — adding entries
+# ---------------------------------------------------------------------------
+
+@test "update_path: adds .luca/tools to PATH when directory exists" {
+    local project="$BATS_TEST_TMPDIR/project"
+    mkdir -p "$project/.luca/tools"
+
+    run bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/bash
+        cd '$project'
+        source '$REPO_ROOT/shell_hook.sh'
+        update_path
+        echo \"\$PATH\"
+    "
+
+    assert_output --partial "$project/.luca/tools"
+}
+
+@test "update_path: idempotent — does not duplicate PATH entry" {
+    local project="$BATS_TEST_TMPDIR/project"
+    mkdir -p "$project/.luca/tools"
+
+    run bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/bash
+        cd '$project'
+        source '$REPO_ROOT/shell_hook.sh' >/dev/null 2>&1
+        update_path
+        update_path
+        # Count occurrences of the tools dir in PATH
+        echo \"\$PATH\" | tr ':' '\n' | grep -c '\.luca/tools' || echo 0
+    "
+
+    assert_output "1"
+}
+
+@test "update_path: PATH unchanged when no .luca/tools in current dir" {
+    local empty_dir="$BATS_TEST_TMPDIR/empty"
+    mkdir -p "$empty_dir"
+
+    run bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/bash
+        cd '$empty_dir'
+        source '$REPO_ROOT/shell_hook.sh'
+        original_path=\$PATH
+        update_path
+        if [ \"\$PATH\" = \"\$original_path\" ]; then echo unchanged; else echo changed; fi
+    "
+
+    assert_output --partial "unchanged"
+}
+
+# ---------------------------------------------------------------------------
+# update_path() — cleanup of stale entries
+# ---------------------------------------------------------------------------
+
+@test "update_path: removes stale .luca/tools entry when navigating away" {
+    local project_a="$BATS_TEST_TMPDIR/project_a"
+    local empty_dir="$BATS_TEST_TMPDIR/other"
+    mkdir -p "$project_a/.luca/tools" "$empty_dir"
+
+    run bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/bash
+        cd '$project_a'
+        source '$REPO_ROOT/shell_hook.sh'
+        update_path
+        cd '$empty_dir'
+        update_path
+        echo \"\$PATH\"
+    "
+
+    refute_output --partial "$project_a/.luca/tools"
+}
+
+@test "update_path: keeps .luca/tools entry when in subdirectory of project" {
+    local project="$BATS_TEST_TMPDIR/myproject"
+    local subdir="$project/src/lib"
+    mkdir -p "$project/.luca/tools" "$subdir"
+
+    run bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/bash
+        cd '$project'
+        source '$REPO_ROOT/shell_hook.sh'
+        update_path
+        cd '$subdir'
+        update_path
+        echo \"\$PATH\"
+    "
+
+    assert_output --partial "$project/.luca/tools"
+}
+
+@test "update_path: non-luca PATH entries are never removed" {
+    local empty_dir="$BATS_TEST_TMPDIR/empty"
+    mkdir -p "$empty_dir"
+
+    run bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/bash
+        export PATH=\"/usr/local/bin:/usr/bin:\$PATH\"
+        cd '$empty_dir'
+        source '$REPO_ROOT/shell_hook.sh'
+        update_path
+        echo \"\$PATH\"
+    "
+
+    assert_output --partial "/usr/local/bin"
+    assert_output --partial "/usr/bin"
+}
+
+# ---------------------------------------------------------------------------
+# install_shell_hook() — bash
+# ---------------------------------------------------------------------------
+
+@test "install_shell_hook: appends hook line to .bashrc" {
+    run bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/bash
+        source '$REPO_ROOT/shell_hook.sh'
+    "
+
+    assert [ -f "$TEST_HOME/.bashrc" ]
+    run grep -c "shell_hook.sh" "$TEST_HOME/.bashrc"
+    assert_output "1"
+}
+
+@test "install_shell_hook: creates .bashrc if it does not exist" {
+    # .bashrc does not exist in TEST_HOME
+    assert [ ! -f "$TEST_HOME/.bashrc" ]
+
+    run bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/bash
+        source '$REPO_ROOT/shell_hook.sh'
+    "
+
+    assert [ -f "$TEST_HOME/.bashrc" ]
+}
+
+@test "install_shell_hook: idempotent — hook line appears exactly once after two sources" {
+    bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/bash
+        source '$REPO_ROOT/shell_hook.sh'
+    "
+    bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/bash
+        source '$REPO_ROOT/shell_hook.sh'
+    "
+
+    run grep -c "shell_hook.sh" "$TEST_HOME/.bashrc"
+    assert_output "1"
+}
+
+# ---------------------------------------------------------------------------
+# install_shell_hook() — zsh
+# ---------------------------------------------------------------------------
+
+@test "install_shell_hook: appends hook line to .zshrc for zsh" {
+    run bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/zsh
+        source '$REPO_ROOT/shell_hook.sh'
+    "
+
+    assert [ -f "$TEST_HOME/.zshrc" ]
+    run grep -c "shell_hook.sh" "$TEST_HOME/.zshrc"
+    assert_output "1"
+}
+
+@test "install_shell_hook: returns 1 for unsupported shell" {
+    run bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/fish
+        source '$REPO_ROOT/shell_hook.sh'
+        install_shell_hook
+        echo exit:\$?
+    "
+
+    assert_output --partial "exit:1"
+}
+
+# ---------------------------------------------------------------------------
+# Shell hook registration
+# ---------------------------------------------------------------------------
+
+@test "bash registration: update_path added to PROMPT_COMMAND on source" {
+    run bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/bash
+        source '$REPO_ROOT/shell_hook.sh'
+        echo \"\$PROMPT_COMMAND\"
+    "
+
+    assert_output --partial "update_path"
+}
+
+@test "bash registration: update_path not added twice on double source" {
+    run bash -c "
+        export HOME='$TEST_HOME'
+        export SHELL=/bin/bash
+        source '$REPO_ROOT/shell_hook.sh' >/dev/null 2>&1
+        source '$REPO_ROOT/shell_hook.sh' >/dev/null 2>&1
+        echo \"\$PROMPT_COMMAND\" | tr ';' '\n' | grep -c 'update_path'
+    "
+
+    assert_output "1"
+}
diff --git a/tests/test_helper/common.bash b/tests/test_helper/common.bash
new file mode 100644
index 0000000..c4f925f
--- /dev/null
+++ b/tests/test_helper/common.bash
@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+
+# Resolve paths relative to this file
+_COMMON_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+TESTS_DIR="$(cd "$_COMMON_DIR/.." && pwd)"
+REPO_ROOT="$(cd "$TESTS_DIR/.." && pwd)"
+FIXTURE_DIR="$TESTS_DIR/fixtures"
+
+common_setup() {
+    export TESTS_DIR REPO_ROOT FIXTURE_DIR
+
+    export TEST_HOME="$BATS_TEST_TMPDIR/home"
+    export TEST_INSTALL_DIR="$BATS_TEST_TMPDIR/bin"
+    mkdir -p "$TEST_HOME/.luca" "$TEST_INSTALL_DIR"
+
+    # Override HOME so scripts write to temp dir instead of real home
+    export HOME="$TEST_HOME"
+
+    # Override INSTALL_DIR so scripts install to temp dir (requires `:- default` patch)
+    export INSTALL_DIR="$TEST_INSTALL_DIR"
+
+    # Override SHELL so scripts don't exit 1 on unsupported shell detection
+    export SHELL=/bin/bash
+
+    # Prepend mocks to PATH so they shadow real commands
+    export PATH="$TESTS_DIR/test_helper/mocks:$TEST_INSTALL_DIR:$PATH"
+
+    # Log file for mock invocations
+    export MOCK_CALL_LOG="$BATS_TEST_TMPDIR/mock_calls.log"
+    touch "$MOCK_CALL_LOG"
+
+    # Sentinel file for sudo mock
+    export MOCK_SUDO_SENTINEL="$BATS_TEST_TMPDIR/sudo_calls.log"
+
+    # Clear all mock control variables
+    unset GITHUB_TOKEN
+    unset MOCK_CURL_BEHAVIOR
+    unset MOCK_GIT_REPO_ROOT
+    unset MOCK_LUCA_VERSION
+    unset MOCK_LUCA_INSTALL_EXIT_CODE
+    unset MOCK_UNAME_OUTPUT
+    unset MOCK_UNZIP_BEHAVIOR
+
+    # Run scripts from temp dir so VERSION_FILE (${PWD}/.luca-version) resolves here
+    cd "$BATS_TEST_TMPDIR"
+}
diff --git a/tests/test_helper/mocks/curl b/tests/test_helper/mocks/curl
new file mode 100755
index 0000000..f34341f
--- /dev/null
+++ b/tests/test_helper/mocks/curl
@@ -0,0 +1,116 @@
+#!/usr/bin/env bash
+# Mock curl - behavior controlled by MOCK_CURL_BEHAVIOR and URL pattern
+
+# Parse arguments: find --output path and URL
+output_path=""
+url=""
+prev_arg=""
+for arg in "$@"; do
+    if [ "$prev_arg" = "--output" ] || [ "$prev_arg" = "-o" ]; then
+        output_path="$arg"
+    fi
+    case "$arg" in
+        http://*|https://*)
+            url="$arg"
+            ;;
+    esac
+    prev_arg="$arg"
+done
+
+# Log this invocation
+echo "curl $url" >> "${MOCK_CALL_LOG:-/dev/null}"
+
+behavior="${MOCK_CURL_BEHAVIOR:-auto}"
+
+# Handle explicit forced failures first
+case "$behavior" in
+    api_fail)
+        exit 1
+        ;;
+    api_empty)
+        if [[ "$url" == *"releases/latest"* ]]; then
+            echo "{}"
+            exit 0
+        fi
+        ;;
+    download_fail)
+        if [[ "$url" == *"releases/download"* ]]; then
+            exit 1
+        fi
+        ;;
+    shell_hook_fail)
+        if [[ "$url" == *"shell_hook.sh"* ]]; then
+            exit 1
+        fi
+        ;;
+    post_checkout_fail)
+        if [[ "$url" == *"post-checkout"* ]]; then
+            exit 1
+        fi
+        ;;
+esac
+
+# Auto behavior based on URL pattern
+if [[ "$url" == *"releases/latest"* ]]; then
+    # GitHub API: return fixture JSON
+    if [ -n "${FIXTURE_DIR:-}" ] && [ -f "$FIXTURE_DIR/api_response_latest.json" ]; then
+        cat "$FIXTURE_DIR/api_response_latest.json"
+    else
+        echo '{"tag_name": "v2.0.0"}'
+    fi
+    exit 0
+
+elif [[ "$url" == *"releases/download"* ]]; then
+    # Binary download: create a placeholder zip
+    if [ -n "$output_path" ]; then
+        touch "$output_path"
+    fi
+    exit 0
+
+elif [[ "$url" == *"shell_hook.sh"* ]]; then
+    # shell_hook.sh download: write a minimal valid bash script
+    if [ -n "$output_path" ]; then
+        cat > "$output_path" << 'MOCK_SHELL_HOOK'
+#!/usr/bin/env bash
+TOOL_FOLDER=".luca"
+
+install_shell_hook() {
+    local shell_rc_file
+    local hook_line="[[ -s \"\$HOME/$TOOL_FOLDER/shell_hook.sh\" ]] && source \"\$HOME/$TOOL_FOLDER/shell_hook.sh\""
+    case "$SHELL" in
+        */bash) shell_rc_file="$HOME/.bashrc" ;;
+        */zsh)  shell_rc_file="$HOME/.zshrc"  ;;
+        *)      return 1 ;;
+    esac
+    touch "$shell_rc_file"
+    if ! grep -Fxq "$hook_line" "$shell_rc_file" 2>/dev/null; then
+        {
+            echo ""
+            echo "# Initialize Luca shell hook (added by Luca installer)"
+            echo "$hook_line"
+        } >> "$shell_rc_file"
+    fi
+}
+
+update_path() { return 0; }
+
+if [[ -n "$BASH_VERSION" && "${BASH_SOURCE[0]}" != "$0" ]] || \
+   [[ -n "$ZSH_VERSION" && "${ZSH_EVAL_CONTEXT}" == *:file:* ]]; then
+    install_shell_hook
+    update_path
+fi
+MOCK_SHELL_HOOK
+        chmod +x "$output_path"
+    fi
+    exit 0
+
+elif [[ "$url" == *"post-checkout"* ]] || [[ "$url" == *"install.sh"* ]]; then
+    # post-checkout or install script download: write a minimal no-op
+    if [ -n "$output_path" ]; then
+        printf '#!/bin/sh\n# mock script\nexit 0\n' > "$output_path"
+        chmod +x "$output_path"
+    fi
+    exit 0
+fi
+
+exit 0
diff --git a/tests/test_helper/mocks/git b/tests/test_helper/mocks/git
new file mode 100755
index 0000000..a778a2b
--- /dev/null
+++ b/tests/test_helper/mocks/git
@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+# Mock git - controlled by MOCK_GIT_REPO_ROOT
+
+echo "git $*" >> "${MOCK_CALL_LOG:-/dev/null}"
+
+# Handle rev-parse --show-toplevel
+if [ "$1" = "rev-parse" ] && [ "$2" = "--show-toplevel" ]; then
+    if [ -n "${MOCK_GIT_REPO_ROOT:-}" ]; then
+        echo "$MOCK_GIT_REPO_ROOT"
+        exit 0
+    else
+        echo "fatal: not a git repository (or any of the parent directories): .git" >&2
+        exit 128
+    fi
+fi
+
+exit 0
diff --git a/tests/test_helper/mocks/luca b/tests/test_helper/mocks/luca
new file mode 100755
index 0000000..6858179
--- /dev/null
+++ b/tests/test_helper/mocks/luca
@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+# Mock luca - controlled by MOCK_LUCA_VERSION and MOCK_LUCA_INSTALL_EXIT_CODE
+
+echo "luca $*" >> "${MOCK_LUCA_CALL_LOG:-/dev/null}"
+
+case "${1:-}" in
+    --version)
+        echo "${MOCK_LUCA_VERSION:-v1.0.0}"
+        exit 0
+        ;;
+    install)
+        exit "${MOCK_LUCA_INSTALL_EXIT_CODE:-0}"
+        ;;
+    *)
+        exit 0
+        ;;
+esac
diff --git a/tests/test_helper/mocks/sudo b/tests/test_helper/mocks/sudo
new file mode 100755
index 0000000..1dfb903
--- /dev/null
+++ b/tests/test_helper/mocks/sudo
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+# Mock sudo - logs call and executes the command as current user
+
+echo "sudo $*" >> "${MOCK_SUDO_SENTINEL:-/dev/null}"
+"$@"
diff --git a/tests/test_helper/mocks/uname b/tests/test_helper/mocks/uname
new file mode 100755
index 0000000..b06b906
--- /dev/null
+++ b/tests/test_helper/mocks/uname
@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Mock uname - returns MOCK_UNAME_OUTPUT (default: Darwin)
+
+echo "${MOCK_UNAME_OUTPUT:-Darwin}"
diff --git a/tests/test_helper/mocks/unzip b/tests/test_helper/mocks/unzip
new file mode 100755
index 0000000..b1f8746
--- /dev/null
+++ b/tests/test_helper/mocks/unzip
@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+# Mock unzip - creates a fake Luca binary in the current directory
+
+echo "unzip $*" >> "${MOCK_CALL_LOG:-/dev/null}"
+
+case "${MOCK_UNZIP_BEHAVIOR:-success}" in
+    success)
+        # Create a fake Luca executable (install.sh looks for ./Luca)
+        printf '#!/usr/bin/env bash\necho "%s"\n' "${MOCK_LUCA_VERSION:-v2.0.0}" > "./Luca"
+        chmod +x "./Luca"
+        exit 0
+        ;;
+    fail)
+        echo "unzip: cannot extract" >&2
+        exit 1
+        ;;
+esac
diff --git a/tests/uninstall.bats b/tests/uninstall.bats
new file mode 100644
index 0000000..e9fe067
--- /dev/null
+++ b/tests/uninstall.bats
@@ -0,0 +1,111 @@
+#!/usr/bin/env bats
+
+load 'test_helper/bats-support/load'
+load 'test_helper/bats-assert/load'
+load 'test_helper/common'
+
+setup() {
+    common_setup
+}
+
+# ---------------------------------------------------------------------------
+# Executable removal
+# ---------------------------------------------------------------------------
+
+@test "executable: removes Luca binary when it exists" {
+    # uninstall.sh uses TOOL_NAME=Luca (uppercase), so binary is $INSTALL_DIR/Luca
+    touch "$TEST_INSTALL_DIR/Luca"
+
+    run bash "$REPO_ROOT/uninstall.sh"
+
+    assert_success
+    assert [ ! -f "$TEST_INSTALL_DIR/Luca" ]
+    assert_output --partial "executable has been removed"
+}
+
+@test "executable: graceful when binary does not exist" {
+    run bash "$REPO_ROOT/uninstall.sh"
+
+    assert_success
+    assert_output --partial "executable not found"
+}
+
+# ---------------------------------------------------------------------------
+# Shell hook removal (bash)
+# ---------------------------------------------------------------------------
+
+@test "bashrc: removes hook line and comment when present" {
+    cp "$FIXTURE_DIR/bashrc_with_hook" "$TEST_HOME/.bashrc"
+
+    run bash "$REPO_ROOT/uninstall.sh"
+
+    assert_success
+    assert_output --partial "Shell hook removed"
+    run grep -c "shell_hook.sh" "$TEST_HOME/.bashrc"
+    assert_output "0"
+}
+
+@test "bashrc: no-op when hook is not in .bashrc" {
+    echo 'export FOO=bar' > "$TEST_HOME/.bashrc"
+
+    run bash "$REPO_ROOT/uninstall.sh"
+
+    assert_success
+    assert_output --partial "No shell hook found"
+}
+
+@test "bashrc: no-op when .bashrc does not exist" {
+    # .bashrc does not exist; TEST_HOME/.bashrc was not created
+
+    run bash "$REPO_ROOT/uninstall.sh"
+
+    assert_success
+    assert_output --partial "Shell configuration file not found"
+}
+
+# ---------------------------------------------------------------------------
+# Shell hook removal (zsh)
+# ---------------------------------------------------------------------------
+
+@test "zshrc: removes hook from .zshrc" {
+    cp "$FIXTURE_DIR/bashrc_with_hook" "$TEST_HOME/.zshrc"
+    export SHELL=/bin/zsh
+
+    run env SHELL=/bin/zsh bash "$REPO_ROOT/uninstall.sh"
+
+    assert_success
+    assert_output --partial "Shell hook removed"
+    run grep -c "shell_hook.sh" "$TEST_HOME/.zshrc"
+    assert_output "0"
+}
+
+@test "unsupported shell: warns but exits 0" {
+    run env SHELL=/bin/fish bash "$REPO_ROOT/uninstall.sh"
+
+    assert_success
+    assert_output --partial "Unsupported shell"
+}
+
+# ---------------------------------------------------------------------------
+# Tool directory removal
+# ---------------------------------------------------------------------------
+
+@test "tool dir: removes ~/.luca directory entirely" {
+    mkdir -p "$TEST_HOME/.luca/tools"
+    touch "$TEST_HOME/.luca/some_config"
+
+    run bash "$REPO_ROOT/uninstall.sh"
+
+    assert_success
+    assert [ ! -d "$TEST_HOME/.luca" ]
+    assert_output --partial "Tool directory has been removed"
+}
+
+@test "tool dir: graceful when ~/.luca does not exist" {
+    rm -rf "$TEST_HOME/.luca"
+
+    run bash "$REPO_ROOT/uninstall.sh"
+
+    assert_success
+    assert_output --partial "Tool directory not found"
+}
diff --git a/uninstall.sh b/uninstall.sh
index 7876819..b283c45 100755
--- a/uninstall.sh
+++ b/uninstall.sh
@@ -8,7 +8,7 @@
 # =============================================================================
 
 TOOL_NAME="Luca"
-INSTALL_DIR="/usr/local/bin"
+INSTALL_DIR="${INSTALL_DIR:-/usr/local/bin}"
 TOOL_FOLDER=".luca"
 TOOL_DIR="$HOME/$TOOL_FOLDER"
 SHELL_HOOK_SCRIPT_PATH="$TOOL_DIR/shell_hook.sh"