code: public JsonFluentAssert isStringEqualTo(String expected) {
          isString();
          Node node = getNode(actual, path);
          if (!node.asText().equals(expected)) {
              failOnDifference(quoteTextValue(expected), quoteTextValue(node.asText()));
          }
          return this;
      }
docs: Fails if the selected JSON is not a String or is not present or the value
  is not equal to expected value.