You want to design a simple web based net worth calculator for people to use. You have a mockup in a spreadsheet - see the Net Worth Tracker tab in this workbook. You will track assets and liabilities only. For your proof of concept, you will populate the rows in the tables by default, the user will not be able to add or remove rows.
Account line amounts should be editable.
When an account line amount is edited, a request should be sent to the server which will calculate the totals and net worth and return them.
The UI will render the calculated amounts upon response from the server.
The entered amounts should be validated to ensure they are numbers, fall within an appropriate range, and are not negative.
The user should be able to add or remove items for assets or liabilities in the UI and save it to the service. Saving in a memory structure is fine, a database or file is fine as well.
The service should include unit tests to cover all API calls.