File upload fields are one of the most vulnerable elements in a Drupal form, highly prone to hack attempts. So these have to undergo thorough rounds of testing to make sure the data that goes in is perfectly safe.
Software Testing is the process carried out during software development, so as to ensure and verify that the product, be it a simple program or an entire Drupal site, developed has all the desired features, performs as expected by the customers and meets all their requirements. It also the ensures the robustness of the product. Here is the Levels of Testing in a Drupal Development Workflow.
For any fresher who has never worked in a live project, the term SDLC, might seem to prevail only in theory. Now is your time, to acquire an in-depth understanding of this cycle which moulds an authentic and concrete software product.