Prefer to use reactor.run for test.

test/async/task.rb

@@ -747,15 +747,14 @@ def sleep_forever
 	with "#result" do
 		it "does not raise exception" do
 			task = reactor.async do
-				# Prevent `io_write` hook being invoked.
-				expect(Console).to receive(:warn).and_return(nil)
-
 				raise "The space time converter has failed."
 			end
 
-			expect do
-				task.wait
-			end.to raise_exception(RuntimeError, message: be =~ /space time converter/)
+			reactor.run do
+				expect do
+					task.wait
+				end.to raise_exception(RuntimeError, message: be =~ /space time converter/)
+			end
 
 			expect(task.result).to be_a(RuntimeError)
 		end