feat(appraisal): resolve appraisal name

spec/spec_helper.rb

@@ -1,5 +1,17 @@
 # frozen_string_literal: true
 
+##
+# NOTE: Appraisal sets `BUNDLE_GEMFILE' env variable.
+# This is how appraisals can be differentiated from each other.
+# https://github.com/thoughtbot/appraisal/blob/v2.4.1/lib/appraisal/command.rb#L36
+#
+# If `BUNDLE_GEMFILE' is an empty string, then `APPRAISAL_NAME' is resolved to an empty string as well.
+# User passed `APPRAISAL_NAME' has a precedence.
+#
+# IMPORTANT: `APPRAISAL_NAME' env variable should be initialized as far as it is possible.
+#
+ENV["APPRAISAL_NAME"] ||= ENV["BUNDLE_GEMFILE"].to_s.then(&File.method(:basename)).then { |name| name.end_with?(".gemfile") ? name.delete_suffix(".gemfile") : "" }
+
 require_relative "coverage_helper"
 
 require "bundler/setup"