CSV export shows raw cents instead of a formatted amount (#62)

src/csv.ts

@@ -1,4 +1,5 @@
 import type { Database } from "bun:sqlite";
+import { formatCents } from "./money/cents.ts";
 
 interface ExpenseRow {
   createdAt: string;
@@ -26,19 +27,14 @@ function fetchExpenseRows(db: Database, groupId: string): 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 stay integer cents
+ * until this output boundary, where `formatCents` renders them as "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 +1,45 @@
+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 { exportCsv } from "../src/csv.ts";
+import { formatCents } from "../src/money/index.ts";
+
+function setupDb(): Database {
+  const db = new Database(":memory:");
+  initSchema(db);
+  seedDemoData(db);
+  return db;
+}
+
+function storedCents(db: Database, groupId: string): number[] {
+  const rows = db
+    .query("SELECT amount_cents as amountCents FROM expenses WHERE group_id = ? ORDER BY created_at ASC")
+    .all(groupId) as { amountCents: number }[];
+  return rows.map((r) => r.amountCents);
+}
+
+describe("exportCsv", () => {
+  test("exportCsv formats the amount column with formatCents", () => {
+    const db = setupDb();
+    const lines = exportCsv(db, "flat-4b").trimEnd().split("\n").slice(1);
+    const amounts = lines.map((line) => line.split(",").at(-1));
+    const cents = storedCents(db, "flat-4b");
+
+    expect(amounts).toEqual(cents.map(formatCents));
+    for (const amount of amounts) {
+      expect(amount).toMatch(/^-?\d+\.\d{2}$/);
+    }
+    expect(amounts[0]).toBe("45.00");
+  });
+
+  test("exportCsv keeps the header and one row per expense", () => {
+    const db = setupDb();
+    const csv = exportCsv(db, "flat-4b");
+    const lines = csv.trimEnd().split("\n");
+
+    expect(lines[0]).toBe("date,payer,description,amount");
+    expect(lines.length - 1).toBe(storedCents(db, "flat-4b").length);
+    expect(csv.endsWith("\n")).toBe(true);
+  });
+});