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Interest Calculator Technical Test

Technical Test

Background

You are provided with an API that calculates either simple or compound interest based on input parameters such as the principal amount, interest rate, duration, and type of interest accrual. The API also performs input validation to ensure all provided parameters are positive and the accrual type is either "simple" or "compound".

Task

Your task is to write automated functional tests to verify the functionality and robustness of this Interest Calculator API. Your tests should cover various scenarios including positive cases, negative cases, and edge cases. Feel free to use any tooling of your choice to demonstrate how you would approach writing automation tests for this application. You should spend no longer than 4 hours on this task and we would rather you complete less functionality to a good standard than rushing to try to complete it all. Show us your workings by initialising a git repo and committing your changes as you go. Your submission should be considered the quality you would expect to open a PR, not to merge one. We don't expect the submission to be production standard or gold plated. The submission will be followed up with a review call where we will ask you to walk us through your solution. We will then ask you to extend it with some additional functionality.

Deliverables

  • A git bundle that contains all your automated tests. This can be done by:
git bundle create name.bundle --all
  • README.md in the git bundle detailing
    • How to set up and run your tests
    • A brief explanation of your testing strategy and tools used
    • Any findings from the testing which you would feedback to developers
  • Submit your sample git bundle emailing it to us (via your recruiter if you have one)

Overview

This Spring Boot application provides an API to calculate interest based on user input. It is designed to handle both simple and compound interest calculations using a set of given parameters. The application is built using Kotlin and leverages the Spring Web dependency for handling HTTP requests.

Features

  • Interest Calculation: Users can calculate either simple or compound interest based on input parameters.
  • Input Validation: Ensures all input values are positive and valid before processing.
  • Detailed Output: The API returns a detailed breakdown including the starting amount, interest accrued, and the final balance.

API Endpoint

URL: /interest/calculation

Method: GET

Query Parameters:

  • amount (BigDecimal): The principal amount.
  • interestRate (BigDecimal): The annual interest rate (in percentage).
  • duration (Integer): The duration of the investment/debt in years.
  • accrualType (String): The type of interest calculation (simple or compound).

Responses:

  • 200 OK: Returns the calculation results.
  • 400 Bad Request: Returns an error message if input validation fails.

Validation

The API performs the following validations:

  • All numeric parameters (amount, interestRate, and duration) must be positive values greater than zero.
  • The accrualType must be either simple or compound. Any other values will result in an error.

Interest Calculation

Simple Interest

Simple interest is calculated using the formula:

Interest = Principal x (Interest Rate / 100) x Time

Where:

  • Principal is the initial amount of money.
  • Interest Rate is the annual interest rate in percentage.
  • Time is the duration the money is invested or borrowed for, in years.

Example:

  • Amount: £1000
  • Interest Rate: 5%
  • Duration: 3 years

Calculation:

  • Interest = 1000 x (5 / 100) x 3 = £150

Compound Interest

Compound interest is calculated using the formula:

Total = Principal x (1 + Interest Rate / 100)^Time

Interest Earned = Total - Principal

Where:

  • Principal is the initial amount of money.
  • Interest Rate is the annual interest rate in percentage.
  • Time is the duration the money is compounded for, in years.

Example:

  • Amount: £1000
  • Interest Rate: 5%
  • Duration: 3 years

Calculation:

  • Total = 1000 x (1 + 5 / 100)^3 ≈ £1157.63
  • Interest Earned = £1157.63 - £1000 = £157.63

Running the Application

Ensure you have Gradle or Maven installed, and run the following command in the root directory of the project:

./gradlew bootRun  # For Gradle users

Testing

You can test the API using tools like Postman or CURL by making requests to http://localhost:8080/interest/calculate with the required query parameters.