Source

File: wp-includes/Requests/Transport/cURL.php

public static function test($capabilities = array()) {
		if (!function_exists('curl_init') || !function_exists('curl_exec')) {
			return false;
		}

		// If needed, check that our installed curl version supports SSL
		if (isset($capabilities['ssl']) && $capabilities['ssl']) {
			$curl_version = curl_version();
			if (!(CURL_VERSION_SSL & $curl_version['features'])) {
				return false;
			}
		}

		return true;
	}