Add performance tests to show difference with/without stop condition

spec/performance_spec.rb

@@ -0,0 +1,51 @@
+require "spec_helper"
+require 'benchmark'
+
+RSpec.describe TappingDevice::Device do
+  let(:devices) do
+    devices = []
+    100.times { devices << TappingDevice::Device.new }
+    devices
+  end
+
+  after do
+    devices.each(&:stop!)
+  end
+
+  context "without stop_when" do
+    it "takes long time when tapping multiple devices" do
+      time = Benchmark.realtime do
+        devices.each do |device|
+          s = Student.new("foo", 10)
+          device.tap_on!(s)
+          10.times { s.name }
+
+          expect(device.calls.count).to eq(10)
+        end
+      end
+      devices.each { |d| d.stop! }
+      expect(time).to be_between(4, 10)
+    end
+  end
+
+  context "with stop_when" do
+    it "takes very short time when tapping multiple devices" do
+      time = Benchmark.realtime do
+        devices.each do |device|
+          device.stop_when do
+            device.calls.count == 10
+          end
+
+          s = Student.new("foo", 10)
+          device.tap_on!(s)
+          10.times { s.name }
+
+          expect(device.calls.count).to eq(10)
+        end
+      end
+
+      devices.each { |d| d.stop! }
+      expect(time).to be_between(0, 1)
+    end
+  end
+end