Issue #3264471 by mcdruid, poker10: DatabaseUpdateTestCase::testExpressionUpdate assertion on number of affected rows fails in PostgreSQL

modules/simpletest/tests/database_test.test

@@ -868,14 +868,30 @@ class DatabaseUpdateTestCase extends DatabaseTestCase {
       ->fields(array('age' => 1))
       ->execute();
 
-    // Ensure that expressions are handled properly.  This should set every
+    // Ensure that expressions are handled properly. This should set every
-    // record's age to a square of itself, which will change only three of the
+    // record's age to a square of itself. The number of affected rows returned
-    // four records in the table since 1*1 = 1. That means only three records
+    // by db_update() will vary across different database engines and versions:
-    // are modified, so we should get back 3, not 4, from execute().
+    // - MySQL / InnoDB: changed rows only
+    // - MySQL / MyISAM: changed rows only
+    // - PostgreSQL: all rows matched by the query
+    // - SQLite: changed rows only (see workaround in UpdateQuery_sqlite)
+    // All database engines will change only three of the four records in the
+    // table since 1*1 = 1. However, the pgsql driver will return the number of
+    // rows matched rather than the number changed.
+    // @see https://www.drupal.org/project/drupal/issues/805858
+    // @see https://www.drupal.org/project/drupal/issues/3264471
+    $connection = Database::getConnection()->getConnectionOptions();
+    $expected_rows = 3;
+    if ($connection['driver'] === 'pgsql') {
+      $expected_rows ++;
+    }
     $num_rows = db_update('test')
       ->expression('age', 'age * age')
       ->execute();
-    $this->assertIdentical($num_rows, 3, 'Number of affected rows are returned.');
+    $this->assertIdentical($num_rows, $expected_rows, 'Number of affected rows are returned.');
+
+    $saved_name = db_query('SELECT name FROM {test} WHERE age = :age', array(':age' => pow(26, 2)))->fetchField();
+    $this->assertIdentical('Paul', $saved_name, 'Successfully updated values using an algebraic expression.');
   }
 }