Part 10 · 1 chapters · ~8 min

Capstone: The Ledger API in C#

The shared ledger API capstone in C# with ASP.NET Core minimal APIs, EF Core and MassTransit: idempotent transfers under 100 concurrent requests, double-entry postings summing to zero, payouts with unknown outcomes via the outbox, and a comparison with the Java and Kotlin capstones.

Acceptance

code

dotnet test --filter Category=Acceptance
#  ✓ 100 concurrent identical POST /v1/transfers → exactly 1 transfer (WebApplicationFactory + Testcontainers)
#  ✓ Σ postings = 0 for every transfer (FsCheck property, 1,000 cases)
#  ✓ payout timed out at the rail → Unknown → only a rail confirmation settles it

// property test with FsCheck
[Property] public bool Postings_sum_to_zero(PositiveInt amount, NonNegativeInt fee) =>
    Ledger.PostingsFor(new Kobo(amount.Get), new Kobo(fee.Get % 5_000)).Sum(p => p.Amount.Value) == 0;

CAPSTONE: THE LEDGER API IN C#

the shared acceptance tests from every language course

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shared contract

The same three acceptance tests as every language capstone, run through WebApplicationFactory against a Testcontainers Postgres.

the shared testsreal Postgres