Assertion
Assertions are checks inside our programs that verify something is the way it supposed to be. they are not used to handle situations or edge case that might come up but rather check mistakes. Assertions are not about testing each corner case in our programs but rather catching mistakes we can easily make.
Mistakes and bad input is part of live. An important part of programming is not only about building the program but also fixing mistakes or bugs in the program
update x set( x, x ,x ,x )