Add basic swarming UI tests

appengine/swarming/ui/README.md

Index: appengine/swarming/ui/README.md
diff --git a/appengine/swarming/ui/README.md b/appengine/swarming/ui/README.md
index 1ca487e22146908e5cfb9c7e4aeb91286d710a36..105fc03160aedb613b9faf35d0adb1b9e1f2af6c 100644
--- a/appengine/swarming/ui/README.md
+++ b/appengine/swarming/ui/README.md
@@ -31,13 +31,29 @@ To access the demo pages on localhost:9050, run
     make run
 
 
+To run tests, run
+
+    make test
+
+
 Prerequisites
 =============
 
-You will need to install node.js, npm, and bower, for example:
+You will need to install recent versions of node.js, npm, bower and (optionally)
+web-component-tester:
 
     sudo apt-get install npm nodejs-legacy
     sudo npm install -g bower
+    sudo npm install -g web-component-tester  #if you want to run tests
+
+If you see errors like
+
+    /usr/lib/node_modules/web-component-tester/bin/wct:21
+    promise.then(() => process.exit(0), () => process.exit(1));
+                  ^
+    SyntaxError: Unexpected token )
+
+when running web-component-tester (wct), upgrade node.
 
 
 If you don't want to install npm globally, try