Is it possible to upload files in the process of an automated test ?
Yes it is possible.
If the file is on a local machine (or a mapped network drive), just type the path to the file into the file upload control.
driver = webdriver.Firefox()
element = driver.find_element_by_id("Upload")
In order to enable the transfer of the file from your local machine to the remote machine so it can be uploaded, you need to set a File Detector:
WebElement upload = driver.findElement(By.id("myfile"));