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add_filter( 'template_include', 'so_25789472_template_include' );

function so_25789472_template_include( $template ) {
  if ( is_singular('product') && (has_term( 'mock', 'product_cat')) ) {
    $template = get_stylesheet_directory() . '/woocommerce/single-product-mock.php';
  } 
  return $template;
}