test(spec): cover computeHomeTotalBalance carrier behaviour

Tests Home sums, carrier passthrough on off-Home steps, the Ledger
scale-mismatch case, and a Home > off-Home > Home sequence.

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

@@ -0,0 +1,97 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+
+import { computeHomeTotalBalance } 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("off Home (no cards) after a Home visit of $30: returns carrier $30", () => {
+  assert.equal(
+    computeHomeTotalBalance({
+      cardBalanceTexts: [],
+      previousCarrier: 3000,
+    }),
+    3000,
+  );
+});
+
+test("off Home (no cards) with carrier still 0: returns 0", () => {
+  assert.equal(
+    computeHomeTotalBalance({
+      cardBalanceTexts: [],
+      previousCarrier: 0,
+    }),
+    0,
+  );
+});
+
+test("sequence: Home $30, off-Home, Home $50 tracks new Home totals", () => {
+  let carrier = 0;
+  carrier = computeHomeTotalBalance({
+    cardBalanceTexts: ["$10.00", "$20.00"],
+    previousCarrier: carrier,
+  });
+  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 = 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 is treated as 0", () => {
+  assert.equal(
+    computeHomeTotalBalance({
+      cardBalanceTexts: [undefined, "$10.00"],
+      previousCarrier: 0,
+    }),
+    1000,
+  );
+});