How to get Selenium to wait for a transition page to redirect before running an assertion
A simple approach would be wait for some "particular" text on that final page, see "waitForText" command for further info on it
To add to John's approach, you can use the Selenium wait mechanism to verify that elements on your final page are present like so:
Java:
WebDriverWait wait = new WebDriverWait(webDriver, 10); // seconds
wait.until(ExpectedConditions.visibilityOfElementLocated(By.id("foo")));
Ruby:
wait = Selenium::WebDriver::Wait.new(timeout: 10) # seconds
wait.until { driver.find_element(id: "foo") }
This will properly follow any redirects involved.
Example from https://code.google.com/p/selenium/wiki/RubyBindings
You could call wait_for_page twice in a row. The first waits for the redirect, the second for the final page.