Selenium tests sometimes fail, sometimes pass

Question

I have created tests using selenium 2, I'm also using the selenium standalone server to run the tests.

The problem is that if I run one test, it works. If I run multiple tests, some of them fail. If I try then to run a failed test, it works.

Could the tests be running on threads? I've used the NUnit GUI, and TeamCity to run the tests ... both give the same results : different tests fail, run again, other tests fail.

Any thoughts ?

EDIT

The tests shouldn't depend on one another. The database is emptied and repopulated for every test. I guess the only problem could be that the database is not emptied correctly ... but then if I run the same test multiple times it should also fail.

EDIT2

The tests fail with "element not found". I'll try and add a "WaitForElement" that retries every few milliseconds and maybe that will fix it.

Answer 1

Without knowing the exact errors that are thrown its hard to say. The normal causes of flakiness tend to be waits are not set to a decent time or the web server can't handle that many requests.

If the DB is on the same machine as the webserver, and why shouldnt it be on a build box, it can be intensive to clear it out.

I would recommend going through each of the errors and making it bullet proof for that and then moving to the next. I know people who run there tests all the time without flakiness so its definitely an environmental thing that can be sorted.