Improve testing infra (#442)

* Add test_in_isolation task to run tests in isolation

This simulates how tests are run in Ruby CI and can detect some issues
before they're merged and break Ruby CI later.

* Run test_in_isolation task on CI

* Fix TestRaiseNoBacktraceException's setup

Author: st0012

.github/workflows/test.yml

@@ -36,8 +36,10 @@ jobs:
       with:
         ruby-version: ${{ matrix.ruby }}
         bundler-cache: true
-    - name: Run test
+    - name: Run tests
       run: bundle exec rake test
+    - name: Run tests in isolation
+      run: bundle exec rake test_in_isolation
   vterm-yamatanooroti:
     name: >-
       vterm-yamatanooroti ${{ matrix.ruby }} ${{ matrix.with_latest_reline && '(latest reline)' || '' }}

Rakefile

@@ -8,6 +8,31 @@ Rake::TestTask.new(:test) do |t|
   t.test_files = FileList["test/irb/test_*.rb"]
 end
 
+# To make sure they have been correctly setup for Ruby CI.
+desc "Run each irb test file in isolation."
+task :test_in_isolation do
+  failed = false
+
+  FileList["test/irb/test_*.rb"].each do |test_file|
+    ENV["TEST"] = test_file
+    begin
+      Rake::Task["test"].execute
+    rescue => e
+      failed = true
+      msg = "Test '#{test_file}' failed when being executed in isolation. Please make sure 'rake test TEST=#{test_file}' passes."
+      separation_line = '=' * msg.length
+
+      puts <<~MSG
+        #{separation_line}
+        #{msg}
+        #{separation_line}
+      MSG
+    end
+  end
+
+  fail "Some tests failed when being executed in isolation" if failed
+end
+
 Rake::TestTask.new(:test_yamatanooroti) do |t|
   t.libs << 'test' << "test/lib"
   t.libs << 'lib'

test/irb/test_raise_no_backtrace_exception.rb

@@ -1,4 +1,5 @@
 # frozen_string_literal: false
+require "tmpdir"
 
 require_relative "helper"