Add test for negative license amount

The function throws an error if the license amount is negative

Author: xetxeberria

exercises/tiered_pricing/solutions/xetxeberria-ts/src/tieredPricing.ts

@@ -7,6 +7,11 @@ const priceTiers = [
 ];
 
 export function tieredPricing(licenseAmount: number): number {
+  if (licenseAmount < 0)
+    throw new Error(
+      "Invalid license amount. License amount can not be negative"
+    );
+
   const licensePrice = calculateLicensePrice(licenseAmount);
 
   return licensePrice * licenseAmount;

exercises/tiered_pricing/solutions/xetxeberria-ts/tests/tieredPricing.test.ts

@@ -28,4 +28,8 @@ describe("TieredPricing should", () => {
   test("return 0 for 0 licenses", async () => {
     expect(tieredPricing(0)).toBe(0);
   });
+
+  test("throw an error if the license amount is negative", async () => {
+    expect(() => tieredPricing(-1)).toThrow(Error);
+  });
 });