demonstrate threading issue adzap#187 in a spec

spec/validates_timeliness/config_and_threading_spec.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+RSpec.describe 'Validates Timeliness threadsafety' do
+  before(:each) do
+    ValidatesTimeliness.setup do |config|
+      config.parser.remove_us_formats
+    end
+  end
+
+  let(:us_date) { '06/30/2016' }
+  let(:eu_date) { '30/06/2016' }
+
+  # (fails with Timeliness >= 0.4 but should be fixed with ValidatesTimeliness?)
+  it "doesn't need re-configuration per thread" do
+    expect(Timeliness.parse(eu_date)).not_to be_nil
+    expect(Timeliness.parse(us_date)).to be_nil
+    threads = []
+    threads << Thread.new { expect(Timeliness.parse(eu_date)).not_to be_nil }
+    threads << Thread.new { expect(Timeliness.parse(us_date)).to be_nil }
+    threads.each(&:join)
+  end
+
+  # (fails with Timeliness < 0.4, fixed with Timeliness >= 0.4)
+  it 'is thread_safe' do
+    threads = []
+    threads << Thread.new do
+      Timeliness.use_euro_formats
+      10_000.times { expect(Timeliness.parse(eu_date)).not_to be_nil }
+    end
+    threads << Thread.new do
+      Timeliness.use_us_formats
+      10_000.times { expect(Timeliness.parse(us_date)).not_to be_nil }
+    end
+    threads.each do |t|
+      t.report_on_exception = false
+      t.join
+    end
+  end
+end