Use rake to run tests

.gitignore

@@ -0,0 +1,2 @@
+*.swp
+*.gem

.vscode/settings.json

@@ -1,4 +1,4 @@
 {
-  "code-runner.customCommand": "ruby test/mutual_recursion_test.rb",
+  "code-runner.customCommand": "rake test",
   "code-runner.runInTerminal": true
 }

Rakefile

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+require 'rake/testtask'
+
+desc 'Run tests'
+task default: 'test'
+
+Rake::TestTask.new do |t|
+  t.test_files = FileList['test/*_test.rb']
+end