test: mortgage calculator unit tests

calc/mortgageCalculator.test.ts

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+import { describe, expect, it } from "vitest";
+import { mortgageCalculator } from "./mortgageCalculator";
+
+describe("mortgageCalculator", () => {
+  it("should calculate an interest only mortgage with the correct payments and pricipal", () => {
+    const result = mortgageCalculator(
+      {
+        homeValue: 150_000,
+        deposit: 15_000,
+        interestRate: 6,
+        years: 25
+      },
+      "interestOnly"
+    );
+
+    expect(result).toMatchObject({
+      homeValue: 150000,
+      deposit: 15000,
+      interestPayments: {
+        yearly: 8100,
+        monthly: 675,
+        period: 675
+      },
+      principal: 135000,
+      years: 25,
+      interestRate: 6
+    });
+  });
+
+  it("should calculate a repayment mortgage with the correct monthly payment and remaining principal rounded to two decimal places", () => {
+    const result = mortgageCalculator(
+      {
+        homeValue: 150_000,
+        deposit: 15_000,
+        interestRate: 6,
+        years: 25
+      },
+      "repayment"
+    );
+
+    expect(result).toMatchObject({
+      deposit: 15000,
+      homeValue: 150000,
+      interestRate: 6,
+      monthlyRepayment: 869.81,
+      principal: 135000,
+      years: 25
+    });
+  });
+});