An ounce of prevention..(Testing)

An ounce of prevention is worth a pound of cure
expecting shocks and disorder is being mature
keep an eye on supected mischievous blur
that way you would often be sure,
your deeds will endure and allure

Non-repeatable reads

Leaving your plate alone
just to bring a spoon?
flies might come by and hover
you'd better always cover

Phantom read

In your house all is orderly

expecting things as early
till appears a phantom
that would not show
unless you let the door open

Single Page application

Reserved places for data_
in reserved rooms for sections,
hollow lonely page.

Observer design pattern

Box all that varies,
and to interface expose

avoid strongly coupled bodies,

in each-other sticking their nose

favor loosely coupled honeys,

for any change they predispose    
                        

for that  subscribe observer worries,
to be notified from their bros

keeping an eye on every wiz,
and every  update they disclose

          

UML class diagram of Observer pattern

Decorator design pattern

Open it to extension

but to modification close,

watch inheriting temptation,
for soon the tree explodes,

use rather wrapping decoration,
with few options compose,

anytime have a new creation,
as you wish as you choose.