Fix additional email order in email sink

tests/unit/messenger_compose_test.php

@@ -227,7 +227,9 @@ public function test_messenger_sends_to_additional_emails() {
         $this->assertEquals('Hello world', $this->email_in_sink_attr($sink, 7, 'subject'));
         $this->assertTrue($this->email_in_sink_body_contains($sink, 7, 'This is one fine body.'));
         $this->assertEquals(get_config('moodle', 'noreplyaddress'), $this->email_in_sink_attr($sink, 7, 'from'));
-        $this->assertEquals('[email protected]', $this->email_in_sink_attr($sink, 7, 'to'));
+        $this->assertContains('[email protected]', $this->email_in_sink_attr_all($sink, 'to'));
+        $this->assertContains('[email protected]', $this->email_in_sink_attr_all($sink, 'to'));
+        $this->assertContains('[email protected]', $this->email_in_sink_attr_all($sink, 'to'));
 
         $this->close_email_sink($sink);
     }

tests/unit/traits/sends_emails.php

@@ -53,6 +53,24 @@ public function email_in_sink_attr($sink, $index, $attr) {
         return $message->$attr;
     }
 
+    /**
+     * Gets a list of messages in the sink and builds an array with an attribute provided.
+     *
+     * @param   phpunit_message_sink  $sink   Message sink.
+     * @param   string                $attr   Name of the attribute.
+     * @return  array                         List of the attributes.
+     */
+    public function email_in_sink_attr_all($sink, $attr) {
+        $result = [];
+        $messages = $sink->get_messages();
+        foreach ($messages as $message) {
+            if (!empty($message->$attr)) {
+                $result[] = $message->$attr;
+            }
+        }
+        return $result;
+    }
+
     public function email_in_sink_body_contains($sink, $index, $bodytext) {
         $messages = $sink->get_messages();