test(folio): pin the window rules and the count invariant

pkg/spec/test/folio-total-balance.test.ts

@@ -1,97 +1,88 @@
 import assert from "node:assert/strict";
 import { test } from "node:test";
 
-import { computeHomeTotalBalance } from "../../../examples/folio/sanderling/predicates.ts";
+import { readHomeTotalBalance } from "../../../examples/folio/sanderling/predicates.ts";
 
-test("on Home with two cards ($10, $20): returns $30", () => {
-  assert.equal(
-    computeHomeTotalBalance({
-      cardBalanceTexts: ["$10.00", "$20.00"],
-      previousCarrier: 0,
-    }),
-    3000,
+test("on Home the app's own total is the reading, the carrier and fresh", () => {
+  assert.deepEqual(
+    readHomeTotalBalance({ onHome: true, totalText: "$30.00", previousCarrier: 0 }),
+    { value: 3000, carrier: 3000, fresh: true },
   );
 });
 
-test("off Home (no cards) after a Home visit of $30: returns carrier $30", () => {
-  assert.equal(
-    computeHomeTotalBalance({
-      cardBalanceTexts: [],
-      previousCarrier: 3000,
-    }),
-    3000,
+test("off Home there is nothing to read, so the carrier is reported unchanged", () => {
+  assert.deepEqual(
+    readHomeTotalBalance({ onHome: false, totalText: undefined, previousCarrier: 3000 }),
+    { value: 3000, carrier: 3000, fresh: false },
   );
 });
 
-test("off Home (no cards) with carrier still 0: returns 0", () => {
-  assert.equal(
-    computeHomeTotalBalance({
-      cardBalanceTexts: [],
-      previousCarrier: 0,
-    }),
-    0,
+test("off Home before any Home visit reports the null carrier, still not fresh", () => {
+  assert.deepEqual(
+    readHomeTotalBalance({ onHome: false, totalText: undefined, previousCarrier: null }),
+    { value: null, carrier: null, fresh: false },
   );
 });
 
-test("sequence: Home $30, off-Home, Home $50 tracks new Home totals", () => {
-  let carrier: number | null = 0;
-  carrier = computeHomeTotalBalance({
-    cardBalanceTexts: ["$10.00", "$20.00"],
-    previousCarrier: carrier,
+test("a negative total parses with its sign", () => {
+  assert.deepEqual(
+    readHomeTotalBalance({ onHome: true, totalText: "-$1,234.56", previousCarrier: 0 }),
+    { value: -123456, carrier: -123456, fresh: true },
+  );
+});
+
+test("a fresh Home total overrides whatever the carrier held", () => {
+  assert.deepEqual(
+    readHomeTotalBalance({ onHome: true, totalText: "$7.50", previousCarrier: 9999 }),
+    { value: 750, carrier: 750, fresh: true },
+  );
+});
+
+// The poisoned carrier. An unreadable Home total is UNKNOWN for that step, so
+// null is reported and the property goes vacuous, but the carrier must keep the
+// last total we actually read. Writing null into the carrier is what used to end
+// the run: off-Home steps hand the carrier straight back, so a single
+// unreadable Home left every later step null.
+test("an unreadable Home total reports null but leaves the carrier intact", () => {
+  assert.deepEqual(
+    readHomeTotalBalance({ onHome: true, totalText: undefined, previousCarrier: 3000 }),
+    { value: null, carrier: 3000, fresh: false },
+  );
+});
+
+test("a garbled Home total is unknown, not zero", () => {
+  assert.deepEqual(
+    readHomeTotalBalance({ onHome: true, totalText: "$", previousCarrier: 3000 }),
+    { value: null, carrier: 3000, fresh: false },
+  );
+});
+
+test("an unreadable Home no longer poisons the steps after it", () => {
+  let carrier: number | null = null;
+  const seen: (number | null)[] = [];
+  const step = (onHome: boolean, totalText: string | undefined) => {
+    const reading = readHomeTotalBalance({ onHome, totalText, previousCarrier: carrier });
+    carrier = reading.carrier;
+    seen.push(reading.value);
+  };
+
+  step(true, "$30.00");
+  step(true, undefined);
+  step(false, undefined);
+  step(false, undefined);
+  step(true, "$50.00");
+
+  assert.deepEqual(seen, [3000, null, 3000, 3000, 5000]);
+});
+
+// The clipped fifth account card that started this: it is not a card reading
+// any more, and the footer total the app renders is unaffected by which cards
+// the viewport happens to fit.
+test("Home total is one node, so an off-screen account cannot change it", () => {
+  const withFiveCards = readHomeTotalBalance({
+    onHome: true,
+    totalText: "$2,589.00",
+    previousCarrier: 0,
   });
-  assert.equal(carrier, 3000);
-  carrier = computeHomeTotalBalance({
-    cardBalanceTexts: [],
-    previousCarrier: carrier,
-  });
-  assert.equal(carrier, 3000);
-  carrier = computeHomeTotalBalance({
-    cardBalanceTexts: ["$20.00", "$30.00"],
-    previousCarrier: carrier,
-  });
-  assert.equal(carrier, 5000);
-});
-
-test("Ledger step (no Home cards) holds the carrier, ignores Ledger balance", () => {
-  let carrier: number | null = 0;
-  carrier = computeHomeTotalBalance({
-    cardBalanceTexts: ["$10.00", "$20.00"],
-    previousCarrier: carrier,
-  });
-  assert.equal(carrier, 3000);
-  carrier = computeHomeTotalBalance({
-    cardBalanceTexts: [],
-    previousCarrier: carrier,
-  });
-  assert.equal(carrier, 3000);
-});
-
-test("negative card balance parses with sign and sums correctly", () => {
-  assert.equal(
-    computeHomeTotalBalance({
-      cardBalanceTexts: ["-$5.00", "$10.00"],
-      previousCarrier: 0,
-    }),
-    500,
-  );
-});
-
-test("single card on Home overrides any previous carrier", () => {
-  assert.equal(
-    computeHomeTotalBalance({
-      cardBalanceTexts: ["$7.50"],
-      previousCarrier: 9999,
-    }),
-    750,
-  );
-});
-
-test("undefined card balance text makes the total unknown, not a partial sum", () => {
-  assert.equal(
-    computeHomeTotalBalance({
-      cardBalanceTexts: [undefined, "$10.00"],
-      previousCarrier: 0,
-    }),
-    null,
-  );
+  assert.deepEqual(withFiveCards, { value: 258900, carrier: 258900, fresh: true });
 });