CSV export shows raw cents instead of a formatted amount (#27)

src/csv.ts

@@ -1,4 +1,5 @@
 import type { Database } from "bun:sqlite";
+import { formatCents } from "./money/index.ts";
 
 interface ExpenseRow {
   createdAt: string;
@@ -26,19 +27,15 @@ 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. The amount column is
+ * formatted as a decimal ("10.00") here, at the output boundary.
  */
 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/cli.test.ts

@@ -38,6 +38,11 @@ describe("splitbill export", () => {
     const output = run(["export", "flat-4b"], setupDb());
     expect(output.split("\n")[0]).toBe("date,payer,description,amount");
   });
+
+  test("formats the amount column as a decimal", () => {
+    const output = run(["export", "flat-4b"], setupDb());
+    expect(output.split("\n").some((line) => line.endsWith(",45.00"))).toBe(true);
+  });
 });
 
 describe("splitbill with no command", () => {

tests/csv.test.ts

@@ -0,0 +1,41 @@
+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 { createExpense } from "../src/expenses.ts";
+
+function setupDb(): Database {
+  const db = new Database(":memory:");
+  initSchema(db);
+  seedDemoData(db);
+  return db;
+}
+
+describe("exportCsv", () => {
+  test("formats the amount column as a decimal via formatCents", () => {
+    const lines = exportCsv(setupDb(), "flat-4b").trim().split("\n");
+    const amounts = lines.slice(1).map((line) => line.split(",").at(-1));
+    expect(amounts.sort()).toEqual(["12.00", "30.00", "45.00"]);
+  });
+
+  test("keeps a trailing zero cent in the amount column", () => {
+    const db = setupDb();
+    createExpense(db, {
+      groupId: "flat-4b",
+      payerId: "flat-priya-id",
+      amountCents: 4550,
+      description: "Water bill",
+      splitAmong: ["flat-priya-id", "flat-imran-id", "flat-sara-id"],
+      createdAt: "2026-09-10T09:00:00.000Z", // after the seeded Flat 4B expenses
+    });
+    const lines = exportCsv(db, "flat-4b").trim().split("\n");
+    expect(lines.at(-1)).toEndWith(",Water bill,45.50");
+  });
+
+  test("keeps the header row and one line per expense", () => {
+    const lines = exportCsv(setupDb(), "flat-4b").trim().split("\n");
+    expect(lines[0]).toBe("date,payer,description,amount");
+    expect(lines.length).toBe(4); // header + 3 seeded Flat 4B expenses
+  });
+});

tests/routes.test.ts

@@ -137,5 +137,6 @@ describe("GET /api/groups/:id/export.csv", () => {
     const lines = text.trim().split("\n");
     expect(lines[0]).toBe("date,payer,description,amount");
     expect(lines.length).toBe(4); // header + 3 seeded Flat 4B expenses
+    expect(lines.some((line) => line.endsWith(",45.00"))).toBe(true);
   });
 });