test: exclude multibyte tests for JRuby

* JRuby doesn't seem to be able to handle method names containing
  multi-byte strings correctly.
* see jruby/jruby#1285
* see jruby/jruby#3880

Author: kenichiice

.github/workflows/test.yml

@@ -27,6 +27,9 @@ jobs:
     - uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
-        bundler-cache: true    
+        bundler-cache: true
     # - run: bundle install
-    - run: bundle exec rake test
+    - if: matrix.ruby != 'jruby'
+      run: bundle exec rake test
+    - if: matrix.ruby == 'jruby'
+      run: bundle exec rake test TESTOPTS='--ignore-name=/multibyte/'

Rakefile

@@ -1,8 +1,9 @@
 require "bundler/gem_tasks"
+require "rake/testtask"
 
-task :default => :test
-
-desc "run unit tests"
-task :test do
-    ruby("test/run-test.rb")
+Rake::TestTask.new(:test) do |t|
+  t.libs << "lib"
+  t.test_files = FileList['test/**/test*.rb']
 end
+
+task :default => :test