Hi Vinayak,
As Preeti said, it is standard SAP behaviour and you cant restrict that except doc type settings with respect to A,K,D,M or S or Validation as I mentioned before.
But, Yes, whether splitting is happening or not that is a thing to test and this cannot have any restriction on the document type vis a vis transaction code.
In short, with doc splitting active and your configuration setting where you assign business transaction variant and transaction variant against the doc types, system mandates certain entries for those doc types..
For example, if you use doc type KR, in SPRO you can see that you must have assigned transaction and variant as 0300/0001. Now, if you check SPRO> Define Business transaction variant, you will see that for 0300/0001 - SAP has made Vendor mandatory, meaning in order to split Vendor must be present in your entry else it wont split.
And in order to test, use doc type KR, and try to post an entry without vendor and the system wont split. This would be your testing. Transaction code cannot have any dependency.. No matter what t-code you use, the postings should be correct with doc type as per doc splitting configuration.
Hope I am able to explain it to you..
Regards,
Kavita