The entire parallel.c reported test coverage is zero:
It seem that it's not covered by the original 924bcf4f commit but I don't
know if it's on purpose. This feature being really new that would be
If it's not, my first idea would be to fix this by adding a simple sql test
in /src/test/regress, in the "sql" and "expected" subdirectories that
explain (cost off) some queries.
I'm also guessing here that we can force a query to have a parallel plan
with some cost magic to avoid dealing with sufficiently large datasets.