In software development and testing, an edge case is a scenario that you may not think of, but still may occur, and your software should be equipped to handle it. For example, you're developing a login system, an edge case could be an extremely long email address or a password consisting of only special characters. Or you're developing a website that sells records, what if someone tries to order 10,000 records at once? Or what if they try to check out with an empty cart? These are edge cases. While they may not happen frequently, your software should be able to handle these unexpected or rare conditions.
Software testing is a process where you check if a software system behaves as expected in different scenarios. Just as software testers should test the regular, expected scenarios, known as “happy paths”, it’s also important to test edge cases, so users are less likely to encounter unexpected errors or crashes, even if they use your software in ways you didn't initially predict. By considering a variety of test cases, you make your software more robust and resilient.
Expected scenario: order 1 or 2 records. (happy path)
Edge case: order 10.000 records at once.