Basic model of a wp-config.php file for different stages

wp-config.php

<?php
/**
 * Load different configuration files for different stages.
 */
if ( file_exists( $local_config = dirname( __FILE__ ) . '/local-config.php' ) ) {
	require $local_config; // Configurations for your local stage only.
	define( 'WP_STAGE', 'local' );
} elseif ( file_exists( $staging_config = dirname( __FILE__ ) . '/staging-config.php' ) ) {
	require $staging_config; // Configurations for your testing stage only.
	define( 'WP_STAGE', 'staging' );
} else {
	define( 'WP_STAGE', 'production' );
}

// Your usual code here...