Here is a description of the difference between using click and clickAndWait in Selenium. This is my response to a question posted on the Software Testing Club.
clickAndWait is used instead of click when loading a new page.
It simply waits for the page finish loading before executing the next command. Because of this, any AJAX or non-page loading actions should use click instead of clickAndWait.
clickAndWait will fail after the timeout setting (default 30 seconds) has been reached. You can change the default timeout, or call setTimeout.
If you have an action that takes time but does not reload the page, it may be necessary to insert a manual wait, or waitForElementPresent. For AJAX requests, you might need to check the document readystate property.
A typical method for testing a login form is to write test methods to validate each field and check for errors. The selenium commands you use for a happy path might be something like this:
open /login type username aaron type password secret clickAndWait loginButton verifyTextPresent Welcome back, Aaron
To check that it gives an error message when you type type wrong password, you could do:
open /login-example type username aaron type password secret clickAndWait loginButton verifyTextPresent invalid password
A variation that checks that a password can only be 8 characters might look like this:
open /login-example type username aaron type password secret123 verifyValue password secret12
open /login-example type username aaron click loginButton waitForElementPresent validation_errors verifyTextPresent password is required
Finally, a test with an ajax call on login might look like this:
open /login-example type username aaron type password wrong click loginButton setTimeout 60000 waitForEval selenium.browserbot.getCurrentWindow().document.readyState == "complete" verifyTextPresent "invalid password"
You can see the sample login page at http://www.one-shore.com/aaron/login-example