ABAP_to_the_Future

Eliminating Dependencies 3.1
3.1 Eliminating Dependencies
In the US show “Jeopardy!,” the contesta nt’s answer must be in the form of a
question.
GAME SHOW HOST: Something that stops you dead in your tracks when you
want to write a test.
CONTESTANT: What is a dependency?
The contestant is correct. But to go into a little more detail, a dependency is what
you have when you want to do a test for your productive code but you can’t—
because the productive code reads from the database or writes to the database or
accesses some external system or sends an email or needs some input from a user
or one of a million other things you cannot or do not want to do in the development
environment.
As an example, consider a monolithic SAP program that schedules feeding time at
the zoo and makes sure all the animals get the right amount and type of food.
Everything works fine. The keepers have somesort of mobile device that they can
query to see what animals need feeding next, and there is some sort of feedback
they have to give after feeding the animal s. They want to keep track of the food
inventory, and so on; none of the details are important for this example.
All is well until one day they get two pandas on loan from China, and the programmer
has to make some changes to accommodate their specific panda-type
needs (e.g., bamboo shoots) without mess ing up all the othe r animals. The programmer
can do a unit test on the panda-specific changes he has made, but how
can he be sure that an unforeseen side effect will not starve the lions, causing
them to break out and eat all the birds and all the monkeys before breaking into
the insect house and crushing and eating the beehive?
Normally, there’s no way to do it. There are just to o many dependencies. The
program needs to read the system time, read the configuration details on what
animal gets fed when, read and write inventory levels, send messages to the zookeepers,
receive and proces s input from those same zookeepers, interface with
assorted external systems, and so on.
However, you really don’t want to risk th e existing system breaking and leading
the lions to dine on finch, chimps, and mushy bees, so how can we enable tests?
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