Before 0681a2dd5a, QCOMPARE'ing types
for which no QTest::toString specialization exists did not output
Actual and Expected lines on failure, as that would only print <null>
for both values (which then look like the same value, confusingly).
Commit 0681a2dd5a changed that behavior,
and started printing the confusing <null> values.
Take care of the logic in the formatFailMessage function: if both values
are nullptr, then print only the variable names, but not the confusing
<null> text representation of the values.
Remove dead and duplicated code related to the formatting logic, add a
self-test function, and update the expected_cmptest files.
Fixes: QTBUG-104867
Pick-to: 6.4
Change-Id: I4be98e79f91196b14690a2cc0a68ffd50b431a45
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
54b276be0b