Citibank coding challenge

This repository presents the solution I developed for the Citibank coding challenge. I completed this challenge on 22 June 2023, as part of my interview for the role of Architecture Lead.

Requirement

A piece of simple library code that accepts a salary in pounds and pence, and returns the amount of tax that is due, in pounds and pence.

Tax is applied in bands.

Tax Bands

• 0 - 10,000: 1.89%
• 10,000 - 20,000: 2.5%
• 20,000 - 50,000: 4.75%
• 50,000 - 100,000: 8.25%
• > 100,000: 10.5%

Bands are not cumulative - ie. a salary of 15,000 falls in the 2.5% band, therefore tax due is 2.5% × 15,000.

Details

• Code must be production ready, using core Java.
• Assume that the library code will be used by another team in their application.
• Work as you would if you were writing this as part of your day job.
• You may make use of resources on the Internet, e.g. Java API, Stack Overflow, etc.

Further assumptions and clarifications from the interviews

• BigDecimal is a good choice for representing money.
• The floor of a band is inclusive. The ceiling of a band is exclusive. For example, a salary of 10,000 falls in the 10,000 - 20,000 band.
• Round HALF_UP to the nearest penny.
• I didn't ask about negative salaries, but I assume that they are not allowed.
• Real world code would have logging, but I didn't add them to the solution because they weren't required.

How to build

The project requires JDK 17. It was built and tested with Eclipse Temurin™. It bundles Gradle Wrapper to simplify the build process.

./gradlew build

How to run tests

To run the tests, run:

./gradlew test

To rerun the tests when all tasks are up-to-date, run:

./gradlew --no-build-cache cleanTest test

This project uses Adarsh Ramamurthy's Gradle Test Logger Plugin to produce more readable test output.

Post interview improvements

1. Implemented the band selection logic using NavigableMap#floorEntry and NavigableMap#ceilingEntry as suggested during the interview.
2. Throw an IllegalArgumentException when the salary is negative.
3. Simplified tests by using ParameterizedTest to test tax calculation for each band.
4. I wrote this README with my recollection of the events, so it might not be 100% accurate.
5. I've added GitHub Actions to run the tests on every push and pull request.
6. Dependabot was enabled to keep dependencies up-to-date