Test doc update (#181)

* Update test doc with the problems faced running e2e test

* update the text

Author: ckshobha

docs/TESTS.md

@@ -3,3 +3,36 @@
 ## End-to-End (e2e) tests
 
 You can run the e2e tests with `yarn e2e`. This will stop all docker containers, clear the necessary ports, start the containers and the app, and then run the tests.
+
+# Problems
+
+## e2e cases failed with "Connection refused! Is selenium server started"
+
+**Problem**:
+
+```
+   { Error [ERR_UNHANDLED_ERROR]: Unhandled error. ([object Object])
+   at ClientManager.emit (events.js:140:19)
+   at Nightwatch.<anonymous> .....
+   .....
+   context:
+   { message: 'Connection refused! Is selenium server started?\n',
+     data: { value: [Object], status: 33 } } }
+   .....
+```
+
+**Solution**:
+```
+  - Ensure the required version of selenium package is installed
+    yarn list | grep selen
+
+  - Ensure to check selenium server is not running prior to starting the e2e tests.
+    ps -ef | grep sele
+
+  - Ensure the server is started when "yarn e2e" is run by running
+    ps -ef | grep sele
+    502 44074 44068   0 12:23PM ttys008    0:00.06 /usr/bin/java -jar ./node_modules/selenium-server/lib/runner/selenium-server-standalone-3.8.1.jar -port 4444
+
+    Ensure the pid on the output matches the one displayed when yarn e2e was started.  
+    Look for line that says "Starting selenium server... started - PID:  44074"
+```