Regarding CVE-2018-17144 and test cases Regarding the serious bug found (CVE-2018-17144) I am note sure if I understand the full scope of it correctly.

As far as I understand, any block containing a double-spend of a transaction output that was spend in any block prior to the mined one would not have been catched as an invalid block?

If that is the case I wonder if the test suite of bitcoin core does not have a test case implemented for this situation?
There are tests for that.  The specifically broken pattern was a block containing a single transaction spending the same output, which originated from an earlier block, twice. Testing it without putting it in a block, or splitting up the double spend across multiple transactions weren't sufficient tests.