diff --git a/install.sh b/install.sh
index 421205c..1de97fb 100755
--- a/install.sh
+++ b/install.sh
@@ -202,7 +202,7 @@ install_run_update_profile() {
 
 install_main() {
     local repo_url="${BASE_INSTALL_REPO_URL:-https://github.com/codeforester/base.git}"
-    local install_dir="${BASE_INSTALL_DIR:-$HOME/work/base}"
+    local install_dir="${BASE_INSTALL_DIR:-${BASE_HOME:-$HOME/work/base}}"
     local branch="${BASE_INSTALL_BRANCH:-}"
     local update_profile="${BASE_INSTALL_UPDATE_PROFILE:-true}"
     BASE_INSTALL_DRY_RUN="${BASE_INSTALL_DRY_RUN:-false}"
diff --git a/tests/install.bats b/tests/install.bats
index fe535fd..3aa4fa5 100644
--- a/tests/install.bats
+++ b/tests/install.bats
@@ -6,7 +6,9 @@ bats_require_minimum_version 1.5.0
 setup() {
     setup_test_tmpdir
     TEST_HOME="$TEST_TMPDIR/home"
-    mkdir -p "$TEST_HOME"
+    TEST_MOCKBIN="$TEST_TMPDIR/mockbin"
+    TEST_COMMAND_LOG="$TEST_TMPDIR/install-commands"
+    mkdir -p "$TEST_HOME" "$TEST_MOCKBIN"
 }
 
 run_installer() {
@@ -15,6 +17,66 @@ run_installer() {
         "$BASE_REPO_ROOT/install.sh" "$@"
 }
 
+create_supported_bash_stub() {
+    cat > "$TEST_MOCKBIN/bash" <<'EOF'
+#!/usr/bin/env bash
+printf '%s\n' "$*" >> "${BASE_INSTALL_TEST_COMMAND_LOG:?}"
+if [[ ! -x "${1:-}" ]]; then
+    printf 'expected executable basectl path, got: %s\n' "${1:-}" >&2
+    exit 1
+fi
+case "${2:-}" in
+    setup|update-profile)
+        exit 0
+        ;;
+    *)
+        printf 'unexpected basectl command: %s\n' "${2:-}" >&2
+        exit 1
+        ;;
+esac
+EOF
+    chmod +x "$TEST_MOCKBIN/bash"
+}
+
+create_install_source_repo() {
+    local source_dir="$TEST_TMPDIR/source-repo"
+
+    git clone "$BASE_REPO_ROOT" "$source_dir" >/dev/null 2>&1
+    git -C "$source_dir" checkout -B master >/dev/null 2>&1
+    printf '%s\n' "$source_dir"
+}
+
+run_real_installer() {
+    run env \
+        HOME="$TEST_HOME" \
+        PATH="/usr/bin:/bin:/usr/sbin:/sbin" \
+        BASE_INSTALL_TEST_BASH_VERSION=32 \
+        BASE_INSTALL_BASH_CANDIDATES="$TEST_MOCKBIN/bash" \
+        BASE_INSTALL_TEST_COMMAND_LOG="$TEST_COMMAND_LOG" \
+        "$BASE_REPO_ROOT/install.sh" "$@"
+}
+
+assert_base_init_loads() {
+    local install_dir="$1"
+    local resolved_install_dir
+    resolved_install_dir="$(cd "$install_dir" && pwd -P)"
+
+    run env -i \
+        HOME="$TEST_HOME" \
+        BASE_HOME="$install_dir" \
+        PATH="/usr/bin:/bin:/usr/sbin:/sbin" \
+        "$BASH" -c '\
+            source "$BASE_HOME/base_init.sh"; \
+            printf "BASE_HOME=%s\n" "$BASE_HOME"; \
+            if declare -F import_base_lib >/dev/null 2>&1; then \
+                printf "IMPORT_BASE_LIB=1\n"; \
+            fi'
+
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"BASE_HOME=$resolved_install_dir"* ]]
+    [[ "$output" == *"IMPORT_BASE_LIB=1"* ]]
+}
+
 @test "installer prints planned actions in dry-run mode" {
     run_installer --dry-run --dir "$TEST_HOME/work/base" --repo-url https://example.test/base.git --no-profile
 
@@ -68,3 +130,97 @@ run_installer() {
     [ "$status" -eq 1 ]
     [[ "$output" == *"exists but is not a Git checkout"* ]]
 }
+
+@test "installer clones and sets up Base in a fresh directory" {
+    create_supported_bash_stub
+    local install_dir="$TEST_HOME/work/base"
+    local repo_url
+    repo_url="$(create_install_source_repo)"
+
+    run_real_installer --dir "$install_dir" --repo-url "$repo_url" --branch master
+
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"Cloning Base into '$install_dir'."* ]]
+    [[ "$output" == *"Running basectl setup."* ]]
+    [[ "$output" == *"Updating shell startup files."* ]]
+    [[ "$output" == *"Base installation is complete."* ]]
+    [ -d "$install_dir/.git" ]
+    [ -x "$install_dir/bin/basectl" ]
+    [ -f "$install_dir/base_init.sh" ]
+    grep -Fqx "$install_dir/bin/basectl setup" "$TEST_COMMAND_LOG"
+    grep -Fqx "$install_dir/bin/basectl update-profile" "$TEST_COMMAND_LOG"
+
+    assert_base_init_loads "$install_dir"
+}
+
+@test "installer reruns idempotently on an existing Base checkout" {
+    create_supported_bash_stub
+    local install_dir="$TEST_HOME/work/base"
+    local repo_url
+    repo_url="$(create_install_source_repo)"
+
+    run_real_installer --dir "$install_dir" --repo-url "$repo_url" --branch master --no-profile
+    [ "$status" -eq 0 ]
+    local installed_head
+    installed_head="$(git -C "$install_dir" rev-parse HEAD)"
+
+    run_real_installer --dir "$install_dir" --repo-url "$repo_url" --branch master --no-profile
+
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"Updating existing Base checkout at '$install_dir'."* ]]
+    [ "$(git -C "$install_dir" rev-parse HEAD)" = "$installed_head" ]
+    [ -x "$install_dir/bin/basectl" ]
+    [ -f "$install_dir/base_init.sh" ]
+}
+
+@test "installer uses BASE_HOME as the default install directory" {
+    create_supported_bash_stub
+    local install_dir="$TEST_HOME/base-home-install"
+    local repo_url
+    repo_url="$(create_install_source_repo)"
+
+    run env \
+        HOME="$TEST_HOME" \
+        BASE_HOME="$install_dir" \
+        PATH="/usr/bin:/bin:/usr/sbin:/sbin" \
+        BASE_INSTALL_TEST_BASH_VERSION=32 \
+        BASE_INSTALL_BASH_CANDIDATES="$TEST_MOCKBIN/bash" \
+        BASE_INSTALL_TEST_COMMAND_LOG="$TEST_COMMAND_LOG" \
+        "$BASE_REPO_ROOT/install.sh" --repo-url "$repo_url" --branch master --no-profile
+
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"Install path: $install_dir"* ]]
+    [ -d "$install_dir/.git" ]
+    [ -x "$install_dir/bin/basectl" ]
+}
+
+@test "installer fails when the target directory cannot be created" {
+    create_supported_bash_stub
+    local parent="$TEST_TMPDIR/unwritable"
+    local install_dir="$parent/base"
+    local repo_url
+    repo_url="$(create_install_source_repo)"
+    mkdir -p "$parent"
+    chmod a-w "$parent"
+
+    run_real_installer --dir "$install_dir" --repo-url "$repo_url" --branch master --no-profile
+    chmod u+w "$parent"
+
+    [ "$status" -ne 0 ]
+    [[ "$output" == *"Permission denied"* || "$output" == *"could not create work tree dir"* ]]
+    [ ! -e "$install_dir" ]
+}
+
+@test "installer leaves basectl executable and base_init loadable after install" {
+    create_supported_bash_stub
+    local install_dir="$TEST_HOME/loadable/base"
+    local repo_url
+    repo_url="$(create_install_source_repo)"
+
+    run_real_installer --dir "$install_dir" --repo-url "$repo_url" --branch master --no-profile
+
+    [ "$status" -eq 0 ]
+    [ -x "$install_dir/bin/basectl" ]
+    [ -f "$install_dir/base_init.sh" ]
+    assert_base_init_loads "$install_dir"
+}