static bool _verifyImage( const QString &testName, QString &report )
{
  QgsRenderChecker checker;
  checker.setControlPathPrefix( QStringLiteral( "data_defined_size_legend" ) );
  checker.setControlName( "expected_" + testName );
  checker.setRenderedImage( _fileNameForTest( testName ) );
  checker.setSizeTolerance( 3, 3 );
  bool equal = checker.compareImages( testName, 500 );
  report += checker.report();
  return equal;
}