feat: run pg_regress tests after installing the last version of the extension (#1826)

We have been testing the extension by running pg_regress tests after the
migration of the extension (from the first available version to the last
one). However, we were not testing the case where the last version of
the extension is installed directly. This change adds a test for that
case.

Author: jfroche

nix/ext/tests/default.nix

@@ -151,7 +151,7 @@ let
           with subtest("Check upgrade path with postgresql 15"):
             test.check_upgrade_path("15")
 
-          with subtest("Check pg_regress with postgresql 15"):
+          with subtest("Check pg_regress with postgresql 15 after extension upgrade"):
             test.check_pg_regress(Path("${psql_15}/lib/pgxs/src/test/regress/pg_regress"), "15", pg_regress_test_name)
 
           last_version = None
@@ -162,18 +162,27 @@ let
             with subtest("Test switch_${pname}_version"):
               test.check_switch_extension_with_background_worker(Path("${psql_15}/lib/${pname}.so"), "15")
 
+          with subtest("Check pg_regress with postgresql 15 after installing the last version"):
+            test.check_pg_regress(Path("${psql_15}/lib/pgxs/src/test/regress/pg_regress"), "15", pg_regress_test_name)
+
           with subtest("switch to postgresql 17"):
             server.succeed(
               f"{pg17_configuration}/bin/switch-to-configuration test >&2"
             )
 
-          with subtest("Check last version of the extension after upgrade"):
+          with subtest("Check last version of the extension after postgresql upgrade"):
             test.assert_version_matches(last_version)
 
           with subtest("Check upgrade path with postgresql 17"):
             test.check_upgrade_path("17")
 
-          with subtest("Check pg_regress with postgresql 17"):
+          with subtest("Check pg_regress with postgresql 17 after extension upgrade"):
+            test.check_pg_regress(Path("${psql_17}/lib/pgxs/src/test/regress/pg_regress"), "17", pg_regress_test_name)
+
+          with subtest("Check the install of the last version of the extension"):
+            test.check_install_last_version("17")
+
+          with subtest("Check pg_regress with postgresql 17 after installing the last version"):
             test.check_pg_regress(Path("${psql_17}/lib/pgxs/src/test/regress/pg_regress"), "17", pg_regress_test_name)
         '';
     };