1 files changed, 38 insertions, 0 deletions
diff --git a/test/spend-budget.test.ts b/test/spend-budget.test.ts
new file mode 100644
index 00000000..81c16b2a
--- /dev/null
+++ b/test/spend-budget.test.ts
@@ -0,0 +1,38 @@
+import { describe, expect, test } from "bun:test";
+import {
+  assertWithinSpendLimit,
+  debitTotal,
+} from "$lib/spend-budget";
+
+describe("NWC budget covers the final captured tip and fees", () => {
+  test("a small invoice with an oversized mutable tip is rejected", () => {
+    expect(
+      debitTotal({ amount: 19, tip: 1_701_450, fee: 0, ourfee: 0 }),
+    ).toBe(1_701_469);
+    expect(() =>
+      assertWithinSpendLimit({
+        amount: 19,
+        tip: 1_701_450,
+        maxTotal: 10_000,
+      }),
+    ).toThrow("Budget exceeded");
+  });
+
+  test("the exact remaining allowance succeeds", () => {
+    expect(
+      assertWithinSpendLimit({
+        amount: 9_000,
+        tip: 500,
+        fee: 400,
+        ourfee: 100,
+        maxTotal: 10_000,
+      }),
+    ).toBe(10_000);
+  });
+
+  test("an unlimited first-party debit remains unaffected", () => {
+    expect(
+      assertWithinSpendLimit({ amount: 19, tip: 1_701_450 }),
+    ).toBe(1_701_469);
+  });
+});