diff --git a/lib/dml/tests/dml_mysqli_read_slave_test.php b/lib/dml/tests/dml_mysqli_read_slave_test.php
index d2d8a952ee7..af55928f384 100644
--- a/lib/dml/tests/dml_mysqli_read_slave_test.php
+++ b/lib/dml/tests/dml_mysqli_read_slave_test.php
@@ -48,12 +48,12 @@ class core_dml_mysqli_read_slave_testcase extends base_testcase {
         $this->assertEquals(0, $DB->perf_get_reads_slave());
 
         $DB->query_start("SELECT GET_LOCK('lock',1)", null, SQL_QUERY_SELECT);
-        $this->assertEquals('test_rw', $DB->get_db_handle());
+        $this->assertTrue($DB->db_handle_is_rw());
         $DB->query_end(null);
         $this->assertEquals(0, $DB->perf_get_reads_slave());
 
         $DB->query_start("SELECT RELEASE_LOCK('lock',1)", null, SQL_QUERY_SELECT);
-        $this->assertEquals('test_rw', $DB->get_db_handle());
+        $this->assertTrue($DB->db_handle_is_rw());
         $DB->query_end(null);
         $this->assertEquals(0, $DB->perf_get_reads_slave());
     }
diff --git a/lib/dml/tests/dml_pgsql_read_slave_test.php b/lib/dml/tests/dml_pgsql_read_slave_test.php
index 8cb49ee128a..dcaef72bb85 100644
--- a/lib/dml/tests/dml_pgsql_read_slave_test.php
+++ b/lib/dml/tests/dml_pgsql_read_slave_test.php
@@ -62,13 +62,13 @@ class core_dml_pgsql_read_slave_testcase extends base_testcase {
         // Read from the non-written to table cursor.
         $sql = 'FETCH 1 FROM crs1';
         $DB->query_start($sql, null, SQL_QUERY_AUX);
-        $this->assertEquals('test_ro', $DB->get_db_handle());
+        $this->assertTrue($DB->db_handle_is_ro());
         $DB->query_end(null);
 
         // Read from the written to table cursor.
         $sql = 'FETCH 1 FROM crs2';
         $DB->query_start($sql, null, SQL_QUERY_AUX);
-        $this->assertEquals('test_rw', $DB->get_db_handle());
+        $this->assertTrue($DB->db_handle_is_rw());
         $DB->query_end(null);
     }
 
@@ -83,7 +83,7 @@ class core_dml_pgsql_read_slave_testcase extends base_testcase {
         $this->assertEquals(0, $DB->perf_get_reads_slave());
 
         $DB->query_start('SELECT pg_whatever(1)', null, SQL_QUERY_SELECT);
-        $this->assertEquals('test_ro', $DB->get_db_handle());
+        $this->assertTrue($DB->db_handle_is_ro());
         $DB->query_end(null);
         $this->assertEquals(1, $DB->perf_get_reads_slave());
     }
@@ -101,7 +101,7 @@ class core_dml_pgsql_read_slave_testcase extends base_testcase {
 
         foreach (['pg_try_advisory_lock', 'pg_advisory_unlock'] as $fn) {
             $DB->query_start("SELECT $fn(1)", null, SQL_QUERY_SELECT);
-            $this->assertEquals('test_rw', $DB->get_db_handle());
+            $this->assertTrue($DB->db_handle_is_rw());
             $DB->query_end(null);
             $this->assertEquals(0, $DB->perf_get_reads_slave());
         }
diff --git a/lib/dml/tests/fixtures/test_moodle_read_slave_trait.php b/lib/dml/tests/fixtures/test_moodle_read_slave_trait.php
index bba77655352..27a729343ee 100644
--- a/lib/dml/tests/fixtures/test_moodle_read_slave_trait.php
+++ b/lib/dml/tests/fixtures/test_moodle_read_slave_trait.php
@@ -46,14 +46,47 @@ trait test_moodle_read_slave_trait {
     // @codingStandardsIgnoreEnd
         parent::__construct($external);
 
+        $rw = fopen("php://memory", 'r+');
+        fputs($rw, 'rw');
+
+        $ro = fopen("php://memory", 'r+');
+        fputs($ro, 'ro');
+
         $this->wantreadslave = true;
-        $this->dbhwrite = 'test_rw';
-        $this->dbhreadonly = 'test_ro';
+        $this->dbhwrite = $rw;
+        $this->dbhreadonly = $ro;
         $this->set_db_handle($this->dbhwrite);
 
         $this->temptables = new moodle_temptables($this);
     }
 
+    /**
+     * Check db handle
+     * @param string $id
+     * @return bool
+     */
+    public function db_handle_is($id) {
+        $dbh = $this->get_db_handle();
+        rewind($dbh);
+        return stream_get_contents($dbh) == $id;
+    }
+
+    /**
+     * Check db handle is rw
+     * @return bool
+     */
+    public function db_handle_is_rw() {
+        return $this->db_handle_is('rw');
+    }
+
+    /**
+     * Check db handle is ro
+     * @return bool
+     */
+    public function db_handle_is_ro() {
+        return $this->db_handle_is('ro');
+    }
+
     /**
      * Upgrade to public
      * @return resource