Avoid deadlock with concurrent test

The sql_query commands on lines 334 and 372 can be executes in parallel during a test and create a failure. With locking the users table this is avoided.

diesel_tests/tests/update.rs

@@ -331,7 +331,8 @@ fn upsert_with_sql_literal_for_target() {
     let connection = &mut connection();
     // This index needs to happen before the insert or we'll get a deadlock
     // with any transactions that are trying to get the row lock from insert
-    diesel::sql_query("CREATE UNIQUE INDEX ON users (name) WHERE name != 'Tess'")
+    // As tests can run concurrently, lock the table of interest.
+    diesel::sql_query("BEGIN; LOCK TABLE users; CREATE UNIQUE INDEX ON users (name) WHERE name != 'Tess'; COMMIT;")
         .execute(connection)
         .unwrap();
     insert_sean_and_tess_into_users_table(connection);
@@ -369,7 +370,8 @@ fn upsert_with_sql_literal_for_target_with_condition() {
     let connection = &mut connection();
     // This index needs to happen before the insert or we'll get a deadlock
     // with any transactions that are trying to get the row lock from insert
-    diesel::sql_query("CREATE UNIQUE INDEX ON users (name) WHERE name != 'Tess'")
+    // As tests can run concurrently, lock the table of interest.
+    diesel::sql_query("BEGIN; LOCK TABLE users; CREATE UNIQUE INDEX ON users (name) WHERE name != 'Tess'; COMMIT;")
         .execute(connection)
         .unwrap();
     insert_sean_and_tess_into_users_table(connection);