code: public SelendroidCapabilities addBootstrapClass(String className) {
      String currentClassNames = getBootstrapClassNames();
      if (currentClassNames == null || currentClassNames.isEmpty()) {
        setCapability(BOOTSTRAP_CLASS_NAMES, className);
      } else {
        setCapability(BOOTSTRAP_CLASS_NAMES, currentClassNames + "," + className);
      }
      return this;
    }
docs: Adds a class to run on app startup. Class names are stored as a string separated by commas.