test: add test for depreciation functions

app/models/Property.test.ts

@@ -1,71 +1,183 @@
 import { Property } from "./Property";
+import { HOUSE_BREAKDOWN_PERCENTAGES, MAINTENANCE_LEVELS } from './constants';
 
-let property: Property;
-
-beforeEach(() => {
-  property = new Property({
-    postcode: "WV8 1HG",
-    houseType: "T",
-    numberOfBedrooms: 2,
-    age: 10,
-    size: 88,
-    maintenancePercentage: 0.02,
-    newBuildPricePerMetre: 2120,
-    averageMarketPrice: 218091.58,
-    itl3: "TLG24",
+describe('Property', () => {
+  beforeEach(() => {
+    property = new Property({
+      postcode: "MK14 7AG",
+      houseType: "T",
+      numberOfBedrooms: 2,
+      age: 10,
+      size: 88,
+      maintenancePercentage: 0.02,
+      newBuildPricePerMetre: 2120,
+      averageMarketPrice: 219135,
+      itl3: "TLJ12",
+    });
   });
-});
-
-it("can be instantiated", () => {
-  expect(property).toBeInstanceOf(Property);
-});
-
-it("correctly calculates the newBuildPrice", () => {
-  expect(property.newBuildPrice).toBeCloseTo(186560);
-});
-
-it("correctly calculates the depreciatedBuildPrice for existing builds (age > 0)", () => {
-  expect(property.depreciatedBuildPrice).toBeCloseTo(172988.92);
-});
-
-it("correctly calculates depreciatedBuildPrice for newbuilds (age = 0)", () => {
-  property = new Property({
-    postcode: "WV8 1HG",
-    houseType: "T",
-    numberOfBedrooms: 2,
-    age: 1,
-    size: 88,
-    maintenancePercentage: 0.02,
-    newBuildPricePerMetre: 2120,
-    averageMarketPrice: 218091.58,
-    itl3: "TLG24",
+
+  let property: Property;
+
+  it("can be instantiated", () => {
+    expect(property).toBeInstanceOf(Property);
+  });
+
+  it("correctly calculates the newBuildPrice", () => {
+    expect(property.newBuildPrice).toBeCloseTo(186560);
+  });
+
+  // 
+  it("correctly calculates the bedWeightedAveragePrice", () => {
+    expect(property.bedWeightedAveragePrice).toBeCloseTo(219135);
+  });
+
+  it("correctly calculates the landPrice", () => {
+    expect(property.landPrice).toBeCloseTo(32575);
+  });
+
+  it("correctly calculates the landToTotalRatio", () => {
+    expect(property.landToTotalRatio).toBeCloseTo(0.1446);
+  });
+
+  it("correctly calculates the values even for number of bedroooms exceeding the max ", () => {
+    property = new Property({
+      postcode: "WV8 1HG",
+      houseType: "T",
+      numberOfBedrooms: 20,
+      age: 11,
+      size: 88,
+      maintenancePercentage: 0.02,
+      newBuildPricePerMetre: 2120,
+      averageMarketPrice: 218091.58,
+      itl3: "TLG24",
+    });
+    expect(property).toBeInstanceOf(Property);
   });
-  expect(property.depreciatedBuildPrice).toBeCloseTo(186560)
-});
-
-it("correctly calculates the bedWeightedAveragePrice", () => {
-  expect(property.bedWeightedAveragePrice).toBeCloseTo(218091.58);
-});
-
-it("correctly calculates the landPrice", () => {
-  expect(property.landPrice).toBeCloseTo(31531.579);
-});
-
-it("correctly calculates the landToTotalRatio", () => {
-  expect(property.landToTotalRatio).toBeCloseTo(0.14);
-});
-
-it("correctly calculates the values even for number of bedroooms exceeding the max ", () => {
-  property = new Property({
-    postcode: "WV8 1HG",
-    houseType: "T",
-    numberOfBedrooms: 20,
-    age: 9,
-    size: 88,
-    maintenancePercentage: 0.02,
-    newBuildPricePerMetre: 2120,
-    averageMarketPrice: 218091.58,
-    itl3: "TLG24",
+
+  it("correctly returns newBuildPrice if newbuild", () => {
+    property = new Property({
+      postcode: "WV8 1HG",
+      houseType: "T",
+      numberOfBedrooms: 20,
+      age: 1,
+      size: 88,
+      maintenancePercentage: 0.02,
+      newBuildPricePerMetre: 2120,
+      averageMarketPrice: 218091.58,
+      itl3: "TLG24",
+    });
+
+    expect(property.depreciatedBuildPrice).toBe(property.newBuildPrice);
+  });
+
+  describe('depreciation calculations (existing build)', () => {
+
+    it("correctly calculates newComponentValue for foundations", () => {
+      const result = property.calculateComponentValue(
+        'foundations',
+        property.newBuildPrice,
+        property.age,
+        MAINTENANCE_LEVELS[0]
+      );
+
+      const expectedNewComponentValue = 
+        property.newBuildPrice * 
+        HOUSE_BREAKDOWN_PERCENTAGES.foundations.percentageOfHouse;
+
+      expect(result.newComponentValue).toBe(expectedNewComponentValue);
+      expect(result.maintenanceAddition).toBe(0); // Foundations should have no maintenance
+    });
+
+    it("correctly calculates depreciationFactor for internal linings", () => {
+      const result = property.calculateComponentValue(
+        'internalLinings',
+        property.newBuildPrice,
+        property.age,
+        MAINTENANCE_LEVELS[0]
+      );
+
+      const expectedDepreciationFactor = 
+        1 - (HOUSE_BREAKDOWN_PERCENTAGES.internalLinings.depreciationPercentageYearly * property.age);
+
+      expect(result.depreciationFactor).toBe(expectedDepreciationFactor);
+    });
+
+    it("correctly calculates maintenanceAddition for electrical appliances", () => {
+      const result = property.calculateComponentValue(
+        'electricalAppliances',
+        property.newBuildPrice,
+        property.age,
+        MAINTENANCE_LEVELS[0]
+      );
+
+      const expectedMaintenanceAddition = 
+        MAINTENANCE_LEVELS[0] * 
+        property.newBuildPrice * 
+        property.age * 
+        HOUSE_BREAKDOWN_PERCENTAGES.electricalAppliances.percentOfMaintenanceYearly;
+
+      expect(result.maintenanceAddition).toBe(expectedMaintenanceAddition);
+    });
+
+    it("correctly calculates depreciatedComponentValue for ventilation services", () => {
+      const result = property.calculateComponentValue(
+        'ventilationServices',
+        property.newBuildPrice,
+        property.age,
+        MAINTENANCE_LEVELS[0]
+      );
+
+      const component = HOUSE_BREAKDOWN_PERCENTAGES.ventilationServices;
+      const newComponentValue = property.newBuildPrice * component.percentageOfHouse;
+      const depreciationFactor = 1 - (component.depreciationPercentageYearly * property.age);
+      const maintenanceAddition = 
+        MAINTENANCE_LEVELS[0] * 
+        property.newBuildPrice * 
+        property.age * 
+        component.percentOfMaintenanceYearly;
+
+      const expectedValue = Math.max(
+        (newComponentValue * depreciationFactor) + maintenanceAddition,
+        0
+      );
+
+      expect(result.depreciatedComponentValue).toBe(expectedValue);
+    });
+
+    it("ensures depreciatedComponentValue never goes below 0", () => {
+      const result = property.calculateComponentValue(
+        'ventilationServices',
+        property.newBuildPrice,
+        100, // High age to test possible negative values
+        MAINTENANCE_LEVELS[0]
+      );
+
+      expect(result.depreciatedComponentValue).toBeGreaterThanOrEqual(0);
+    });
+
+    it('should calculate correct depreciation for a 10-year-old house', () => {
+      // Calculate the expected value manually
+      const newBuildPrice = property.newBuildPrice;
+      let expectedDepreciatedPrice = 0;
+
+      // Calculate for each component (mimicking calculateComponentValue())
+      for (const [key, value] of Object.entries(HOUSE_BREAKDOWN_PERCENTAGES)) {
+        const newComponentValue = newBuildPrice * value.percentageOfHouse;
+        const depreciationFactor = 1 - (value.depreciationPercentageYearly * property.age);
+
+        const maintenanceAddition = (key === 'foundations' || key === 'structureEnvelope') 
+          ? 0 
+          : MAINTENANCE_LEVELS[0] * newBuildPrice * property.age * value.percentOfMaintenanceYearly;
+
+        const depreciatedComponentValue = Math.max(
+          (newComponentValue * depreciationFactor) + maintenanceAddition,
+          0
+        );
+
+        expectedDepreciatedPrice += depreciatedComponentValue;
+      }
+
+      expect(property.depreciatedBuildPrice).toBeCloseTo(Number(expectedDepreciatedPrice.toFixed(2)));
+    });
   });
-  expect(property).toBeInstanceOf(Property);
-});
+});