Login page with Selenium webdriver
The method names are consistent, but usually camelcase is advocated.
Indentation is inconsistent, but maybe that's from pasting it here?
Variables like usern and userp are bad, why not name and
password or something that's readable?
Why is the window maximised?  The site doesn't look that's necessary
for anything.
Consider having a login method instead of repeating the same code
five times, e.g. login.login("admin", "admin").
Extract common code to a new method.  That is, for four of the five
tests it could just be checkFailedLogin("foo", "bar").
IDs are/should be unique to elements in HTML, so the XPath is way too
complicated, consider just By.id (and By.className and By.name
for that matter).
Also consider returning the expected page from that method so that
it's clear from the code, MainPage main = login.login(...); and have
it raise an exception if the new page doesn't match what was expected
(e.g. we usually have an invisible value unique to each page to
identify it in tests, but there are probably other ways to do that).