Addition of test cases

[ilyas829]

• Positive as well as negative test cases are important to handle breakage of code at users perspective
• I have added few test cases (pytest test function ) to handle few Issues.
• please review my PR and merge it

1. https://github.com/SUSE/BCI-dockerfile-generator/pull/1797
2. https://github.com/SUSE/BCI-dockerfile-generator/pull/1796
3. https://github.com/SUSE/BCI-dockerfile-generator/pull/1795
4. https://github.com/SUSE/BCI-dockerfile-generator/pull/1794

If more test should be added please give your suggestions or feedback @dirkmueller .

[alexandrevicenzi]

There's no need to create an issue for open PRs, we can see that PRs are open.