In Solidity 0.4.10, the following functions were created: assert(), require(), and revert(). Here we'll discuss the assert function and how to use it.
Formally said, the assert() function is meant to assert invariants; informally said, assert() is an overly assertive bodyguard that protects your contract, but steals your gas in the process. Properly functioning contracts should never reach a failing assert statement. If you've reached a failing assert statement, you've either improperly used assert(), or there is a bug in your contract that puts it in an invalid state.
If the condition checked in the assert() is not actually an invariant, it's suggested that you replace it with a require() statement.