code: public WebDriver getDriver() {
          // Driver's name is retrieved by system properties
          String driverName = Context.getBrowser();
          driverName = driverName != null ? driverName : DEFAULT_DRIVER;
          WebDriver driver = null;
          if (!drivers.containsKey(driverName)) {
              try {
                  driver = generateWebDriver(driverName);
              } catch (final TechnicalException e) {
                  logger.error("error DriverFactory.getDriver()", e);
              }
          } else {
              driver = drivers.get(driverName);
          }
          return driver;
      }
docs: Get selenium driver. Drivers are lazy loaded.
  
  @return selenium driver