diff --git a/clean_files.txt b/clean_files.txt
index 54180c19..07417266 100644
--- a/clean_files.txt
+++ b/clean_files.txt
@@ -137,7 +137,6 @@ plugins/available/zoxide.plugin.bash
 test/plugins/alias-completion.plugin.bats
 test/run
 test/test_helper.bash
-test/test_helper_libs.bash
 
 # themes
 #
diff --git a/test/run b/test/run
index 14d83950..91732a3b 100755
--- a/test/run
+++ b/test/run
@@ -2,17 +2,23 @@
 test_directory="$(cd "$(dirname "$0")" && pwd)"
 bats_executable="${test_directory}/../test_lib/bats-core/bin/bats"
 
+# Locate ourselves for easy reference.
+export MAIN_BASH_IT_DIR="${test_directory%/*}"
+export MAIN_BASH_IT_GITDIR="${MAIN_BASH_IT_DIR}/.git"
+
+# Make sure BATS is available:
 git submodule init && git submodule update
 
-if [[ -z "${BASH_IT}" ]]; then
-	BASH_IT="$(cd "${test_directory}" && dirname "${PWD}")"
-	export BASH_IT
+# Warn user that tests run from the current git HEAD
+if ! git diff --quiet; then
+	echo "${BASH_SOURCE##*/}: your worktree is dirty; uncommitted changes will *not* be tested!"
 fi
 
-if [[ -z "$1" ]]; then
+# Which tests do we run?
+if [[ $# -eq '0' ]]; then
 	test_dirs=("${test_directory}"/{bash_it,completion,install,lib,plugins,themes})
 else
-	test_dirs=("$1")
+	test_dirs=("$@")
 fi
 
 # Make sure that the `parallel` command is installed,
@@ -41,5 +47,5 @@ if command -v parallel &> /dev/null \
 		"${test_dirs[@]}"
 else
 	# Run `bats` in single-threaded mode.
-	exec "$bats_executable" ${CI:+--tap} "${test_dirs[@]}"
+	exec "$bats_executable" "${CI:+--tap}" "${test_dirs[@]}"
 fi
diff --git a/test/test_helper.bash b/test/test_helper.bash
old mode 100755
new mode 100644
index 06660979..919e7559
--- a/test/test_helper.bash
+++ b/test/test_helper.bash
@@ -1,105 +1,117 @@
-#!/usr/bin/env bats
-load "${BASH_IT}/vendor/github.com/erichs/composure/composure.sh"
+# shellcheck shell=bash
 
-unset BASH_IT_THEME
-unset GIT_HOSTING
-unset NGINX_PATH
-unset IRC_CLIENT
-unset TODO
-unset SCM_CHECK
-unset BASH_IT_AUTOMATIC_RELOAD_AFTER_CONFIG_CHANGE
-
-export TEST_MAIN_DIR="${BATS_TEST_DIRNAME}/.."
-export TEST_DEPS_DIR="${TEST_DEPS_DIR-${TEST_MAIN_DIR}/../test_lib}"
-
-# be independent of git's system configuration
-export GIT_CONFIG_NOSYSTEM
-
-load "${TEST_DEPS_DIR}/bats-support/load.bash"
-load "${TEST_DEPS_DIR}/bats-assert/load.bash"
-load "${TEST_DEPS_DIR}/bats-file/load.bash"
-
-# support 'plumbing' metadata
-cite _about _param _example _group _author _version
-cite about-alias about-plugin about-completion
-
-local_setup() {
-	true
+function setup_file() {
+	common_setup_file
 }
 
-local_teardown() {
-	true
-}
+function common_setup_file() {
+	# export *everything* to subshells, needed to support tests
+	set -a
 
-# This function sets up a local test fixture, i.e. a completely
-# fresh and isolated Bash-it directory. This is done to avoid
-# messing with your own Bash-it source directory.
-# If you need this, call it in your .bats file's `local_setup` function.
-setup_test_fixture() {
-	mkdir -p "$BASH_IT"
-	lib_directory="$(cd "$(dirname "$0")" && pwd)"
-	local src_topdir="$lib_directory/../../../.."
+	# Locate ourselves for easy reference.
+	TEST_MAIN_DIR="${MAIN_BASH_IT_DIR:-${BATS_TEST_DIRNAME?}/../..}/test"
+	TEST_DEPS_DIR="${MAIN_BASH_IT_DIR:-${TEST_MAIN_DIR}/..}/test_lib"
 
-	if command -v rsync &> /dev/null; then
-		# Use rsync to copy Bash-it to the temp folder
-		rsync -qavrKL -d --delete-excluded --exclude=.git --exclude=helper.bash --exclude=enabled "$src_topdir" "$BASH_IT"
-	else
-		rm -rf "$BASH_IT"
-		mkdir -p "$BASH_IT"
+	# Load the BATS modules we use:
+	load "${TEST_DEPS_DIR}/bats-support/load.bash"
+	load "${TEST_DEPS_DIR}/bats-assert/load.bash"
+	load "${TEST_DEPS_DIR}/bats-file/load.bash"
 
-		find "$src_topdir" \
-			-mindepth 1 -maxdepth 1 \
-			-not -name .git \
-			-exec cp -r {} "$BASH_IT" \;
-	fi
-
-	rm -rf "$BASH_IT"/enabled
-	rm -rf "$BASH_IT"/aliases/enabled
-	rm -rf "$BASH_IT"/completion/enabled
-	rm -rf "$BASH_IT"/plugins/enabled
-
-	mkdir -p "$BASH_IT"/enabled
-	mkdir -p "$BASH_IT"/aliases/enabled
-	mkdir -p "$BASH_IT"/completion/enabled
-	mkdir -p "$BASH_IT"/plugins/enabled
-
-	# Some tests use the BASH_IT_TEST_HOME variable, e.g. install/uninstall
-	export BASH_IT_TEST_HOME="$TEST_TEMP_DIR"
-}
-
-setup() {
-	# The `temp_make` function from "bats-file" requires the tralston/bats-file fork,
-	# since the original ztombol/bats-file's `temp_make` does not work on macOS.
-	TEST_TEMP_DIR="$(temp_make --prefix 'bash-it-test-')"
-	export TEST_TEMP_DIR
-
-	export BASH_IT_TEST_DIR="${TEST_TEMP_DIR}/.bash_it"
-
-	export BASH_IT_ROOT="${BASH_IT_TEST_DIR}/root"
-	export BASH_IT=$BASH_IT_TEST_DIR
-
-	mkdir -p -- "${BASH_IT_ROOT}"
+	# shellcheck disable=SC2034 # Clear any inherited environment:
+	XDG_DUMMY="" BASH_IT_DUMMY=""    # avoid possible invalid reference:
+	unset "${!XDG_@}" "${!BASH_IT@}" # unset all BASH_IT* and XDG_* variables
+	unset GIT_HOSTING NGINX_PATH IRC_CLIENT TODO SCM_CHECK
 
 	# Some tools, e.g. `git` use configuration files from the $HOME directory,
-	# which interferes with our tests. The only way to keep `git` from doing this
-	# seems to set HOME explicitly to a separate location.
+	# which interferes with our tests. The only way to keep `git` from doing
+	# this seems to set HOME explicitly to a separate location.
 	# Refer to https://git-scm.com/docs/git-config#FILES.
-	unset XDG_CONFIG_HOME
-	export HOME="${TEST_TEMP_DIR}"
+	readonly HOME="${BATS_SUITE_TMPDIR?}"
 	mkdir -p "${HOME}"
 
 	# For `git` tests to run well, user name and email need to be set.
 	# Refer to https://git-scm.com/docs/git-commit#_commit_information.
 	# This goes to the test-specific config, due to the $HOME overridden above.
-	git config --global user.name "John Doe"
-	git config --global user.email "johndoe@example.com"
+	git config --global user.name "Bash It BATS Runner"
+	git config --global user.email "bats@bash.it"
+	git config --global advice.detachedHead false
+	git config --global init.defaultBranch "master"
 
+	# Locate the temporary folder, avoid double-slash.
+	BASH_IT="${BATS_FILE_TMPDIR//\/\///}/.bash_it"
+
+	# This sets up a local test fixture, i.e. a completely fresh and isolated Bash-it directory. This is done to avoid messing with your own Bash-it source directory.
+	git --git-dir="${MAIN_BASH_IT_GITDIR?}" worktree add -d "${BASH_IT}"
+
+	load "${BASH_IT?}/vendor/github.com/erichs/composure/composure.sh"
+	# support 'plumbing' metadata
+	cite _about _param _example _group _author _version
+	cite about-alias about-plugin about-completion
+
+	# Run any local test setup
+	local_setup_file
+	set +a # not needed, but symetiric!
+}
+
+# Load standard _Bash It_ libraries
+function setup_libs() {
+	local lib
+	# Use a loop to allow convenient short-circuiting for some test files
+	for lib in "log" "utilities" "helpers" "search" "preexec" "colors"; do
+		load "${BASH_IT?}/lib/${lib}.bash" || return
+		# shellcheck disable=SC2015 # short-circuit if we've reached the requested library
+		[[ "${lib}" == "${1:-}" ]] && return 0 || true
+	done
+	return 0
+}
+
+function local_setup_file() {
+	true
+}
+
+function local_setup() {
+	true
+}
+
+function local_teardown() {
+	true
+}
+
+function clean_test_fixture() {
+	rm -rf "${BASH_IT_CONFIG?}/enabled"
+	rm -rf "${BASH_IT_CONFIG?}/aliases/enabled"
+	rm -rf "${BASH_IT_CONFIG?}/completion/enabled"
+	rm -rf "${BASH_IT_CONFIG?}/plugins/enabled"
+
+	rm -rf "${BASH_IT_CONFIG?}/tmp/cache"
+	rm -rf "${BASH_IT_CONFIG?}/profiles"/test*.bash_it
+}
+
+function setup_test_fixture() {
+	mkdir -p "${BASH_IT_CONFIG?}/enabled"
+	mkdir -p "${BASH_IT_CONFIG?}/aliases/enabled"
+	mkdir -p "${BASH_IT_CONFIG?}/completion/enabled"
+	mkdir -p "${BASH_IT_CONFIG?}/plugins/enabled"
+}
+
+function setup() {
+	# be independent of git's system configuration
+	export GIT_CONFIG_NOSYSTEM
+	# Locate the temporary folder:
+	BASH_IT_CONFIG="${BASH_IT?}" #"${BATS_TEST_TMPDIR//\/\///}"
+	export XDG_CACHE_HOME="${BATS_TEST_TMPDIR?}"
+
+	setup_test_fixture
 	local_setup
 }
 
-teardown() {
+function teardown() {
+	unset GIT_CONFIG_NOSYSTEM
 	local_teardown
-
-	rm -rf "${BASH_IT_TEST_DIR}"
-	temp_del "${TEST_TEMP_DIR}"
+	clean_test_fixture
+}
+
+function teardown_file() {
+	# This only serves to clean metadata from the real git repo.
+	git --git-dir="${MAIN_BASH_IT_GITDIR?}" worktree remove -f "${BASH_IT?}"
 }
diff --git a/test/test_helper_libs.bash b/test/test_helper_libs.bash
deleted file mode 100644
index fac2a9eb..00000000
--- a/test/test_helper_libs.bash
+++ /dev/null
@@ -1,8 +0,0 @@
-# shellcheck shell=bash
-
-load "${BASH_IT}/lib/log.bash"
-load "${BASH_IT}/lib/utilities.bash"
-load "${BASH_IT}/lib/helpers.bash"
-load "${BASH_IT}/lib/search.bash"
-load "${BASH_IT}/lib/preexec.bash"
-load "${BASH_IT}/lib/colors.bash"