Project · Rust Programming

Project: parallel UPI settlement with full tests

Projectexpert· about 7 hours· 7 steps

The brief

A payment aggregator settles each merchant's UPI collections at the end of the day. You write a library crate that parses transaction lines, adds up successful payments per merchant on several threads (a channel collects the partial totals) and counts outcomes in an Arc<Mutex<Stats>>. Then you prove it with unit tests (including should_panic), an integration test, doc tests, cargo clippy -D warnings and cargo fmt --check.

Why it matters

Fintech and payments companies in India process crores of UPI transactions a day, and settlement code must be both fast and exactly right. Splitting work across threads safely, and backing every function with tests that a CI pipeline runs on each pull request, is what Rust teams in these companies do daily.

Skills you practise

a library crate (src/lib.rs) with a thin main.rs
thread::spawn with move closures
mpsc channels and dropping the sender
Arc<Mutex<T>> shared state
#[test], assert_eq! and #[should_panic]
integration tests in tests/
doc tests in /// comments
cargo clippy -- -D warnings and cargo fmt --check

You need

Rust stable installed with rustup, with the clippy and rustfmt components (rustup component add clippy rustfmt)
A terminal and an editor

What you will have at the end

An upi_settle crate: a library with threaded settlement and shared counters, a thin main.rs, six unit tests, an integration test, two doc tests, and a clean cargo fmt --check and cargo clippy -D warnings run.

How it is marked (rubric, 100 points)

Correct and deterministicTotals of Rs 95.00, Rs 680.50 and Rs 300.00, 9 successes and 2 failures, the same on every run and with any number of threads.	30
Safe concurrencyThe extra sender is dropped so the receiving loop ends, Arc<Mutex> holds the shared counters, and every thread is joined before results are read.	25
Tests at every levelUnit tests with edge cases and should_panic, an integration test through the public API, and doc examples that run.	30
Professional finishcargo fmt --check and cargo clippy --all-targets -- -D warnings both clean.	15

0/7 steps done

Step 1 of 7

A library crate with tested parsing

parse_txn works and three unit tests pass.

Run cargo new upi_settle, then add src/lib.rs next to main.rs: a package can hold a library and a binary, and main.rs uses the library by its name (upi_settle::...). Keeping the logic in the library makes it testable without a terminal. Write parse_txn: split the line on commas, return TxnError::WrongFieldCount unless there are 4 parts, parse the amount (BadAmount on failure), and match the status text (BadStatus for anything but SUCCESS or FAILED). Then write three tests in the tests module: parses_valid_line, rejects_bad_amount and rejects_unknown_status. Run only the library's unit tests with cargo test --lib. Leave tests/settlement.rs for step 5: it uses items you have not written yet.

Run this on your machine, then paste the output below

$ cargo test --lib

Your notes: src/lib.rs, src/main.rs, tests/settlement.rs

Write down each command you ran. It goes into your project summary.