Thread-safety for async config methods

spec/support/examples/async.rb

@@ -34,6 +34,60 @@ RSpec.shared_examples 'async' do |request_args: -> {}|
         end.to_not change(instance, :async).from(described_class.default_async_job)
       end
     end
+
+    context 'in multi-threaded environment' do
+      it 'changes only in current thread' do
+        thread = nil
+        expect do
+          thread = Thread.new do
+            expect do
+              subject.call(false) do
+                expect(subject[]).to eq false
+              end
+            end.to_not change(instance, :async).from(described_class.default_async_job)
+            sleep 0.2
+          end
+        end.to_not change(instance, :async).from(described_class.default_async_job)
+        thread.join
+      end
+
+      it 'uses default value after block' do
+        thread = Thread.new do
+          subject.call(false) {}
+          expect { sleep 0.2 }.to change(instance, :async).
+            from(described_class.default_async_job).to(nil)
+        end
+        sleep 0.1
+        instance.async = nil
+        thread.join
+      end
+    end
+  end
+
+  describe '#async=' do
+    subject { ->(val = new_val) { instance.async = val } }
+    let(:async) {}
+
+    context 'when true is given' do
+      let(:new_val) { true }
+      it { should change(instance, :async).to described_class.default_async_job }
+    end
+
+    context 'when false is given' do
+      let(:new_val) { false }
+      it { should change(instance, :async).to false }
+    end
+
+    context 'when string is given' do
+      let(:new_val) { 'Telegram::Bot::Client' }
+      it { should change(instance, :async).to Object.const_get(new_val) }
+    end
+
+    context 'in multi-threaded environment' do
+      subject { ->(val = new_val) { Thread.new { instance.async = val }.join } }
+      let(:new_val) { true }
+      it { should change(instance, :async).to described_class.default_async_job }
+    end
   end
 
   describe '.default_async_job' do