Need advice on writing better test cases.

[Ben Finney]

Anubhav Yadav <anubhav.yadav at gmx.com> writes:

> I want to write more test cases, specially that rely on database
> insertions and reads and file IO.

Thanks for taking seriously the importance of test cases for your code!

One important thing to recognise is that a unit test is only one type of
test. It tests one unit of code, typically a function, and should assert
exactly one clearly true-or-false result of calling that code unit.

If you have a function and you want to assert *that function's*
behaviour, you can avoid external dependencies during the test run by
providing fake resources. These can be mocks (e.g. with ‘unittest.mock’)
or other fake resources that are going to behave exactly how you want,
for the purpose of testing the code unit.

Unit test cases:

* Exercise a small unit of code in isolation.
* Each test exactly one obvious behavour of the code unit.
* Aim to have exactly one reason the test case can fail.

Because they are isolated and test a small code unit, they are typically
*fast* and can be run very often, because the entire unit test suite
completes in seconds.

> How to test if things are going into the database properly or not?

That is *not* a unit test; it is a test that one part of your code
has the right effect on some other part of the system. This meets the
description not of a unit test but of an integration test.

These integration tests, because they will likely be a lot slower than
your unit tests, should be in a separate suite of integration tests, to
be run when the time is available to run them.

Integration tests:

* Exercise many code units together.
* Typically make an assertion about the *resulting state* of many
  underlying actions.
* Can have many things that can cause the test case to fail.

> (mysql/mongo). I want to be able to create a test database environment
> as simple as possible. Create and delete the test environment before
> each functional test case is run.

One good article discussion how to make integration tests, specifically
for database integration with your app, is this one
<URL:https://julien.danjou.info/blog/2014/db-integration-testing-strategies-python>.

I hope that helps.

-- 
 \         “The enjoyment of one's tools is an essential ingredient of |
  `\             successful work.” —Donald Knuth, _The Art of Computer |
_o__)                                                     Programming_ |
Ben Finney