postgresqlTestHook: run postgresqlTestSetupPost hook after setting up

doc/hooks/postgresql-test-hook.section.md

···
  - `postgresqlEnableTCP`: set to `1` to enable TCP listening. Flaky; not recommended.
  - `postgresqlStartCommands`: defaults to `pg_ctl start`.
 
+## Hooks {#sec-postgresqlTestHook-hooks}
+
+A number of additional hooks are ran in postgresqlTestHook
+
+ - `postgresqlTestSetupPost`: ran after postgresql has been set up.
+
 ## TCP and the Nix sandbox {#sec-postgresqlTestHook-tcp}
 
 `postgresqlEnableTCP` relies on network sandboxing, which is not available on macOS and some custom Nix installations, resulting in flaky tests.

pkgs/build-support/setup-hooks/postgresql-test-hook/postgresql-test-hook.sh

···
   header 'setting up postgresql'
   eval "$postgresqlTestSetupCommands"
 
+  runHook postgresqlTestSetupPost
+
 }
 
 postgresqlStop() {

pkgs/build-support/setup-hooks/postgresql-test-hook/test.nix

···
     INSERT INTO hello VALUES ('it '||'worked');
     SELECT * FROM hello;
   '';
+  postgresqlTestSetupPost = ''
+    TEST_POST_HOOK_RAN=1
+  '';
   checkPhase = ''
     runHook preCheck
     psql <$sqlPath | grep 'it worked'
···
     runHook postCheck
   '';
   installPhase = ''
-    [[ $TEST_RAN == 1 ]]
+    [[ $TEST_RAN == 1 && $TEST_POST_HOOK_RAN == 1 ]]
     touch $out
   '';
 }