So you need to be expert in coding, also in order to test the codes at github?
Not ordinary guy like me can check bugs or back door in the code.
Not exactly. You should at least know how to run test cases by installing required dependencies to test Bitcoin Core. Apart from this, you should build the wallet from source. As far as Core is concerned, functional test cases were already written in python which makes you easier to test the code without having any prior advanced knowledge in code.
Here is the guide to build Core in Unix and Windows :
Unix and
Windows Once you have built the wallet from source, start your learning curve by running
example_test.py I hope it would be easier for you to understand.
But for one to write functional tests, you should know python at least at a basic level. Most of the altcoins are somehow a clone of bitcoin code. So they would be following the same strategy of tests for testing the source code. But, to develop a wallet application for Bitcoin you need to have a command over the Bitcoin Source Code.