CSV export shows raw cents instead of a formatted amount (#186)

src/csv.ts

@@ -1,4 +1,5 @@
 import type { Database } from "bun:sqlite";
+import { formatCents } from "./money/index.ts";
 
 interface ExpenseRow {
   createdAt: string;
@@ -25,20 +26,13 @@ function fetchExpenseRows(db: Database, groupId: string): ExpenseRow[] {
     .all(groupId) as ExpenseRow[];
 }
 
-/**
- * Build the CSV export for a group's expenses.
- *
- * SEEDED DEFECT (issue #3): the amount column prints the raw integer cents
- * (e.g. "1000") instead of a formatted amount ("10.00"). Baseline tests
- * only check the header row and the row count, not the amount column's
- * formatting, so this ships undetected. The fix should reuse
- * `formatCents` from src/money (see .claude/skills/handling-money).
- */
+/** Build the CSV export for a group's expenses; amounts are formatted as decimals ("10.00"). */
 export function exportCsv(db: Database, groupId: string): string {
   const rows = fetchExpenseRows(db, groupId);
   const header = "date,payer,description,amount\n";
   const lines = rows.map(
-    (r) => `${r.createdAt},${csvEscape(r.payerName)},${csvEscape(r.description)},${r.amountCents}`,
+    (r) =>
+      `${r.createdAt},${csvEscape(r.payerName)},${csvEscape(r.description)},${formatCents(r.amountCents)}`,
   );
   return header + lines.join("\n") + (lines.length > 0 ? "\n" : "");
 }

tests/csv.test.ts

@@ -0,0 +1,73 @@
+import { describe, expect, test } from "bun:test";
+import { Database } from "bun:sqlite";
+import { initSchema } from "../src/db.ts";
+import { seedDemoData } from "../src/seed.ts";
+import { createExpense } from "../src/expenses.ts";
+import { exportCsv } from "../src/csv.ts";
+
+function setupDb() {
+  const db = new Database(":memory:");
+  initSchema(db);
+  seedDemoData(db);
+  return db;
+}
+
+function dataRows(csv: string): string[][] {
+  return csv
+    .trim()
+    .split("\n")
+    .slice(1)
+    .map((line) => line.split(","));
+}
+
+describe("exportCsv", () => {
+  test("exportCsv formats the amount column as a decimal", () => {
+    const rows = dataRows(exportCsv(setupDb(), "flat-4b"));
+    expect(rows.map((r) => r[3])).toEqual(["45.00", "12.00", "30.00"]);
+  });
+
+  test("exportCsv keeps two decimal places", () => {
+    const db = setupDb();
+    const flatIds = ["flat-priya-id", "flat-imran-id", "flat-sara-id"];
+    createExpense(db, {
+      groupId: "flat-4b",
+      payerId: "flat-priya-id",
+      amountCents: 1005,
+      description: "Milk",
+      splitAmong: flatIds,
+      createdAt: "2026-09-10T09:00:00.000Z",
+    });
+    createExpense(db, {
+      groupId: "flat-4b",
+      payerId: "flat-imran-id",
+      amountCents: 1050,
+      description: "Bread",
+      splitAmong: flatIds,
+      createdAt: "2026-09-11T09:00:00.000Z",
+    });
+    const rows = dataRows(exportCsv(db, "flat-4b"));
+    expect(rows.slice(-2).map((r) => r[3])).toEqual(["10.05", "10.50"]);
+  });
+
+  test("exportCsv formats an amount under one dollar with a leading zero", () => {
+    const db = setupDb();
+    createExpense(db, {
+      groupId: "flat-4b",
+      payerId: "flat-priya-id",
+      amountCents: 5,
+      description: "Sticker",
+      splitAmong: ["flat-priya-id"],
+      createdAt: "2026-09-12T09:00:00.000Z",
+    });
+    const rows = dataRows(exportCsv(db, "flat-4b"));
+    expect(rows.at(-1)?.[3]).toBe("0.05");
+  });
+
+  test("exportCsv keeps header and row count", () => {
+    const csv = exportCsv(setupDb(), "flat-4b");
+    const lines = csv.trim().split("\n");
+    expect(lines[0]).toBe("date,payer,description,amount");
+    expect(lines).toHaveLength(4);
+    expect(lines[1]).toBe("2026-09-01T09:00:00.000Z,Priya,Electricity bill,45.00");
+  });
+});