Sometimes validate constraint would fail like this:
```diff
validatable_constraint_8000016 | t
(10 rows)
DROP TABLE constrained_table;
+ERROR: deadlock detected
+DETAIL: Process 16602 waits for ShareRowExclusiveLock on relation 56258 of database 16384; blocked by process 16601.
+Process 16601 waits for AccessShareLock on relation 56120 of database 16384; blocked by process 16602.
+HINT: See server log for query details.
DROP TABLE referenced_table CASCADE;
DROP TABLE referencing_table;
DROP SCHEMA validate_constraint CASCADE;
-NOTICE: drop cascades to 3 other objects
+NOTICE: drop cascades to 4 other objects
DETAIL: drop cascades to type constraint_validity
drop cascades to view constraint_validations_in_workers
drop cascades to view constraint_validations
+drop cascades to table constrained_table
SET search_path TO DEFAULT;
```
Source:
https://github.com/citusdata/citus/actions/runs/6708383699?pr=7291
This change fixes that by not running together with the
foreign_key_to_reference_table test anymore. In passing it also
simplifies dropping of the test its resources.
* Fix incorrect join related fields
Ruleutils expect to give the original index of join columns hence we
should consider the dropped columns while setting the fields in
SetJoinRelatedFieldsCompat.
* add some more tests for joins
* Move tests to join.sql and create a utility function
It was possible to get an assertion error, if a DML command was
cancelled that opened a connection and then "ROLLBACK TO SAVEPOINT" was
used to continue the transaction. The reason for this was that canceling
the transaction might leave the `claimedExclusively` flag on for (some
of) it's connections.
This caused an assertion failure because `CanUseExistingConnection`
would return false and a new connection would be opened, and then there
would be two connections doing DML for the same placement. Which is
disallowed. That this situation caused an assertion failure instead of
an error, means that without asserts this could possibly result in some
visibility bugs, similar to the ones described
https://github.com/citusdata/citus/issues/3867
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