code: public static void checkState(
        boolean expression,
        @NullableDecl String errorMessageTemplate,
        @NullableDecl Object... errorMessageArgs) {
      if (!expression) {
        throw new IllegalStateException(lenientFormat(errorMessageTemplate, errorMessageArgs));
      }
    }
docs: Ensures the truth of an expression involving the state of the calling instance, but not
  involving any parameters to the calling method.
  
  @param expression a boolean expression
  @param errorMessageTemplate a template for the exception message should the check fail. The
  message is formed by replacing each {@code %s} placeholder in the template with an
  argument. These are matched by position - the first {@code %s} gets {@code
  errorMessageArgs[0]}, etc. Unmatched arguments will be appended to the formatted message in
  square braces. Unmatched placeholders will be left as-is.
  @param errorMessageArgs the arguments to be substituted into the message template. Arguments
  are converted to strings using {@link String#valueOf(Object)}.
  @throws IllegalStateException if {@code expression} is false
  @see Verify#verify Verify.verify()