Add EvalPlanQual delete returning isolation test

Author: Andres Freund
Reviewed-by: Pavel Borisov
Discussion: https://www.postgresql.org/message-id/flat/CAPpHfdua-YFw3XTprfutzGp28xXLigFtzNbuFY8yPhqeq6X5kg%40mail.gmail.com

src/test/isolation/expected/eval-plan-qual.out

@@ -746,6 +746,36 @@ savings  |    600|    1200
 (2 rows)
 
 
+starting permutation: read wx2 wb1 c2 c1 read
+step read: SELECT * FROM accounts ORDER BY accountid;
+accountid|balance|balance2
+---------+-------+--------
+checking |    600|    1200
+savings  |    600|    1200
+(2 rows)
+
+step wx2: UPDATE accounts SET balance = balance + 450 WHERE accountid = 'checking' RETURNING balance;
+balance
+-------
+   1050
+(1 row)
+
+step wb1: DELETE FROM accounts WHERE balance = 600 RETURNING *; <waiting ...>
+step c2: COMMIT;
+step wb1: <... completed>
+accountid|balance|balance2
+---------+-------+--------
+savings  |    600|    1200
+(1 row)
+
+step c1: COMMIT;
+step read: SELECT * FROM accounts ORDER BY accountid;
+accountid|balance|balance2
+---------+-------+--------
+checking |   1050|    2100
+(1 row)
+
+
 starting permutation: upsert1 upsert2 c1 c2 read
 step upsert1: 
 	WITH upsert AS

src/test/isolation/specs/eval-plan-qual.spec

@@ -76,6 +76,8 @@ setup		{ BEGIN ISOLATION LEVEL READ COMMITTED; }
 step wx1	{ UPDATE accounts SET balance = balance - 200 WHERE accountid = 'checking' RETURNING balance; }
 # wy1 then wy2 checks the case where quals pass then fail
 step wy1	{ UPDATE accounts SET balance = balance + 500 WHERE accountid = 'checking' RETURNING balance; }
+# wx2 then wb1 checks the case of re-fetching up-to-date values for DELETE ... RETURNING ...
+step wb1	{ DELETE FROM accounts WHERE balance = 600 RETURNING *; }
 
 step wxext1	{ UPDATE accounts_ext SET balance = balance - 200 WHERE accountid = 'checking' RETURNING balance; }
 step tocds1	{ UPDATE accounts SET accountid = 'cds' WHERE accountid = 'checking'; }
@@ -353,6 +355,8 @@ permutation wx1 delwcte c1 c2 read
 # test that a delete to a self-modified row throws error when
 # previously updated by a different cid
 permutation wx1 delwctefail c1 c2 read
+# test that a delete re-fetches up-to-date values for returning clause
+permutation read wx2 wb1 c2 c1 read
 
 permutation upsert1 upsert2 c1 c2 read
 permutation readp1 writep1 readp2 c1 c2