Add a TODO.

src/Tests/FillPdfAdminIdTest.php

@@ -43,6 +43,7 @@ class FillPdfAdminIdTest extends FileManagedTestBase {
     $this->drupalPostForm('admin/structure/fillpdf', $edit, 'Upload');
     $this->assertResponse(200, 'Received a 200 response for posted test file.');
     // Get the fid of the uploaded file to construct the link.
+    // @todo: This should be an entity query.
     $max_fid_after = db_query('SELECT MAX(fid) AS fid FROM {file_managed}')->fetchField();
     $this->drupalGet('admin/structure/fillpdf/' . $max_fid_after);
     $this->assertResponse(200, 'Received a 200 response for fillPDF Edit link.');