/testing

docs/src/snippets/modules.test.ts

// import { expectPlan, memoryAdapters } from "pricemeter/testing";
const mem = memoryAdapters({
  rates: { "otp/sms": (dims) => (dims.country === "TR" ? flat(20_000) : null) }, // a Rate, or a function of (dims, ctx, at)
  prepaid: true,
  balances: { acme: 1_000_000 },
  periodOf: (at) => monthKey({ at }), // usedSoFar per (account, meter, month)
});
const metering = buildMetering().refs(["otp_send"]).meter("otp/sms", ["country"]).bind(mem);

const { plan } = await metering.plan.observe("otp/sms", { country: "TR" }, 2, { type: "otp_send", id: "m1" }, { accountId: "acme" }, { at });
expectPlan(plan, {
  ledger: [{ op: "charge", amount: 40_000 }], //        only the fields you give are compared…
  usage: [{ meter: "otp/sms", dims: { country: "TR" } }], // …but the row count must match
});

mem.store.available("acme"); // 1_000_000 — plan.* never commits
mem.store.used("acme", "otp/sms", at); // 0

pricemeter/testing gives tests, examples and these docs three things.

memoryAdapters(opts)

An in-memory getRate + commit + store that follows the adapter contract: all or nothing, idempotent on (refType, refId), InsufficientCredit when prepaid and short.

Option	Meaning	Default
rates	meter → a Rate or (dims, ctx, at) => Rate | { rate, usedSoFar?, carry? } | null. Meters not listed have no price	{}
prepaid	Balance gate	false (postpaid)
balances	Account → starting balance (micro-units)	{}
periodOf	at → period key; usedSoFar is counted per (account, meter, period)	one lifetime period "*"

When an answer has no usedSoFar, getRate fills it from the usage rows it wrote (per meter, without dimensions; A100). store exposes usage, ledger, account(id) ({ balance, reserved }), available(id), used(account, meter, period?), credit(account, amount), setRate(meter, rate?) and commits (the number of commit calls, no-op retries included).

expectPlan(plan, expected)

A framework-free plan assertion: rows are compared in order and partially (only the fields you give), but the row count must match. It throws at the first difference, showing the actual row; it works under vitest, jest, node:test or bun test.

commitContract({ make, prepaid? })

The contract every commit must pass: writing rows, a repeated (refType, refId) being a no-op, a negative charge crediting, hold/capture/release accounting, release after a retried hold, and — when prepaid — insufficient balance writing nothing. Returns { ok, checks: [{ name, ok, error? }] }. Usage: Writing adapters.

How you’d do it without this

In tests you can use your real adapter: for SQLite, new DatabaseSync(":memory:") is fast and gives the same results as pricemeter/sqlite. Instead of expectPlan, your framework’s toMatchObject works (check the row count separately). The memory adapter’s real value is wiring a tariff to a counter without writing getRate, and being the shortest readable reference for the contract.