chore: Export BASE_DIR environment variable

New users to `asdf` who wish to contribute will run into the following
errors when running `./scripts/test.bash`:

```
 ✗ help should show dummy plugin help specific to version when version is present [7]
   (from function `setup_asdf_dir' in file test/test_helpers.bash, line 16,
    from function `setup' in test file test/help_command.bats, line 6)
     `setup_asdf_dir' failed
   mkdir: cannot create directory ‘/w spacetest_help_should_show_dummy_plugin_help_specific_to_version_when_version_is_present’: Permission denied
```

This is due to paths within the various test suites relying on the
`BASE_DIR` environment variable, which is not set by default.

This pull request modifies `scripts/test.bash` to correctly export
`BASE_DIR`

Note: I am a long-time asdf user, who would like to contribute to the
project and noticed this while setting up my dev environment on an
up-to-date Arch Linux system. My intention is to work on this issue:

#2042

Author: lukebakken

scripts/test.bash

@@ -1,7 +1,6 @@
 #!/usr/bin/env bash
 
 set -euo pipefail
-IFS=$'\n\t'
 
 print.info() {
   printf '[INFO] %s\n' "$1"
@@ -11,18 +10,21 @@ print.error() {
   printf '[ERROR] %s\n' "$1" >&2
 }
 
-{
-  repo_dir=$(git rev-parse --show-toplevel)
-  current_dir=$(pwd -P)
-  if [ "$repo_dir" != "$current_dir" ]; then
-    print.error "This scripts requires execution from the repository root directory."
-    printf "\t%s\t%s\n" "Repo root dir:" "$repo_dir"
-    printf "\t%s\t%s\n\n" "Current dir:" "$current_dir"
-    exit 1
-  fi
-}
+BASE_DIR="$(git rev-parse --show-toplevel)"
+readonly BASE_DIR
+export BASE_DIR
+
+current_dir="$(pwd -P)"
+readonly current_dir
+
+if [[ $BASE_DIR != "$current_dir" ]]; then
+  print.error "This script requires execution from the repository root directory."
+  printf "\t%s\t%s\n" "asdf repo root dir:" "$BASE_DIR" >&2
+  printf "\t%s\t%s\n\n" "current dir:" "$current_dir" >&2
+  exit 1
+fi
 
-test_directory="./test"
+readonly test_directory="$BASE_DIR/test"
 bats_options=(--timing --print-output-on-failure)
 
 if command -v parallel >/dev/null; then
@@ -35,5 +37,5 @@ else
   print.info "For faster test execution, install GNU parallel."
 fi
 
-print.info "Running Bats in directory '${test_directory}' with options:" "${bats_options[@]}"
+print.info "Running Bats in directory '${test_directory}' with options: '${bats_options[*]}'"
 bats "${bats_options[@]}" "${test_directory}"