test: a virtual object test for AMM pools. (#5224)

* feat: first pass at VO and DVO test harnesses

Closes #4997

* docs: add documentation

* test: a virtual object test for AMM pools.

see: #5207

Pretty rudimentary.  It just sees that the objects come back. The test
fails when I manually remove (tested) stuff from state.

There's one test that changed state is persisted: I update the
notifier, and verify that on revival, the count has increased.

A plausible next test would be to add liquidity, but that's a bunch
more work.

* chore: review-inspired cleanups.

Co-authored-by: Chip Morningstar <chip@fudco.com>

packages/run-protocol/test/test-voPool.js

@@ -0,0 +1,89 @@
+// @ts-check
+
+import { runVOTest, test } from '@agoric/swingset-vat/tools/vo-test-harness.js';
+import { setupZCFTest } from '@agoric/zoe/test/unitTests/zcf/setupZcfTest.js';
+import buildManualTimer from '@agoric/zoe/tools/manualTimer.js';
+import { makeIssuerKit } from '@agoric/ertp';
+
+import { definePoolKind } from '../src/vpool-xyk-amm/pool.js';
+import { makeAmmParamManager } from '../src/vpool-xyk-amm/params.js';
+
+const voPoolTest = async (t, mutation, postTest) => {
+  let makePool;
+  const { zoe, zcf } = await setupZCFTest();
+  const invitation = await zcf.makeInvitation(() => {}, 'fake invitation');
+  const paramManager = await makeAmmParamManager(zoe, 25n, 5n, invitation);
+  const { brand: centralBrand } = makeIssuerKit('central');
+  const { brand: secondaryBrand } = makeIssuerKit('secondary');
+  const quoteIssuerKit = makeIssuerKit('Quotes');
+  const liquidityZcfMint = await zcf.makeZCFMint('Liquidity');
+  const { userSeat: poolSeatP } = zcf.makeEmptySeatKit();
+  const { zcfSeat: protocolSeatP } = zcf.makeEmptySeatKit();
+  const [poolSeat, protocolSeat] = await Promise.all([
+    poolSeatP,
+    protocolSeatP,
+  ]);
+
+  const defineVirtualPoolKind = () => {
+    const timer = buildManualTimer(t.log);
+
+    const paramAccessor = paramManager.readonly();
+
+    return definePoolKind(
+      zcf,
+      centralBrand,
+      timer,
+      quoteIssuerKit,
+      paramAccessor,
+      protocolSeat,
+    );
+  };
+
+  const state = {};
+  const testVPool = async (context, phase) => {
+    const { pool, singlePool } = context;
+    if (phase === 'before') {
+      state.notifier = pool.getNotifier();
+      state.toCentralPA = pool.getToCentralPriceAuthority();
+      state.singlePool = pool.getVPool();
+      state.liquidityIssuer = pool.getLiquidityIssuer();
+      mutation(context);
+    } else if (phase === 'after') {
+      const newNotifier = pool.getNotifier();
+      t.is(state.notifier, newNotifier);
+      t.is(state.toCentralPA, pool.getToCentralPriceAuthority());
+      t.is(state.singlePool, singlePool);
+      t.is(state.liquidityIssuer, pool.getLiquidityIssuer());
+      t.truthy(postTest(context));
+    }
+  };
+
+  const prepare = () => {
+    makePool = defineVirtualPoolKind();
+  };
+
+  const makeTestObject = () => {
+    return makePool(liquidityZcfMint, poolSeat, secondaryBrand);
+  };
+
+  await runVOTest(t, prepare, makeTestObject, testVPool);
+};
+
+const noOp = () => {};
+
+test.serial('unchanged', async t => {
+  await voPoolTest(t, noOp, () => true);
+});
+
+test.serial('one update', async t => {
+  await voPoolTest(
+    t,
+    context => {
+      return context.pool.updateState();
+    },
+    async context => {
+      const notification = await context.pool.getNotifier().getUpdateSince();
+      t.is(notification.updateCount, 2);
+    },
+  );
+});