test-contexts.php

<?php
/**
 * See which routes support which contexts
 *
 * Run with `wp eval-file test-contexts.php --skip-wordpress`
 */

$response = WP_CLI\Utils\http_request( 'GET', 'http://wordpress-develop.dev/wp-json' );
$body = json_decode( $response->body, true );
$data = array();
foreach( $body['routes'] as $route => $values ) {
	if ( empty( $values['endpoints'][0]['args']['context'] ) ) {
		continue;
	}
	$data[] = array(
		'route'           => $route,
		'default_context' => $values['endpoints'][0]['args']['context']['default'],
		'enum'            => ! empty( $values['endpoints'][0]['args']['context']['enum'] ) ? implode( ', ', $values['endpoints'][0]['args']['context']['enum'] ) : '',
		);
}

WP_CLI\Utils\format_items( 'table', $data, array( 'route', 'default_context', 'enum' ) );