diff --git a/tests/billing.test.js b/tests/billing.test.js
new file mode 100644
index 0000000..26d9740
--- /dev/null
+++ b/tests/billing.test.js
@@ -0,0 +1,28 @@
+import { calculateCost } from "../libs/billing-lib";
+
+test("Lowest tier", () => {
+  const storage = 10;
+
+  const cost = 4000;
+  const expectedCost = calculateCost(storage);
+
+  expect(cost).toEqual(expectedCost);
+});
+
+test("Middle tier", () => {
+  const storage = 100;
+
+  const cost = 20000;
+  const expectedCost = calculateCost(storage);
+
+  expect(cost).toEqual(expectedCost);
+});
+
+test("Highest tier", () => {
+  const storage = 101;
+
+  const cost = 10100;
+  const expectedCost = calculateCost(storage);
+
+  expect(cost).toEqual(expectedCost);
+});