feat: create maintenance vars test

for ForecastParameters file

app/models/ForecastParameters.test.ts

@@ -0,0 +1,28 @@
+import { createForecastParameters, DEFAULT_FORECAST_PARAMETERS } from "./ForecastParameters";
+
+it("can create default forecast parameters", () => {
+  const params = createForecastParameters(DEFAULT_FORECAST_PARAMETERS.maintenancePercentage);
+  expect(params).toBeDefined();
+});
+
+it("correctly sets maintenance percentage while keeping defaults", () => {
+  const customMaintenance = 0.015;
+  const params = createForecastParameters(customMaintenance);
+
+  expect(params.maintenancePercentage).toBe(customMaintenance);
+  expect(params.incomeGrowthPerYear).toBe(DEFAULT_FORECAST_PARAMETERS.incomeGrowthPerYear);
+  expect(params.rentGrowthPerYear).toBe(DEFAULT_FORECAST_PARAMETERS.rentGrowthPerYear);
+  expect(params.constructionPriceGrowthPerYear).toBe(DEFAULT_FORECAST_PARAMETERS.constructionPriceGrowthPerYear);
+  expect(params.propertyPriceGrowthPerYear).toBe(DEFAULT_FORECAST_PARAMETERS.propertyPriceGrowthPerYear);
+  expect(params.yearsForecast).toBe(DEFAULT_FORECAST_PARAMETERS.yearsForecast);
+  expect(params.affordabilityThresholdIncomePercentage).toBe(DEFAULT_FORECAST_PARAMETERS.affordabilityThresholdIncomePercentage);
+});
+
+it("handles different maintenance percentage values", () => {
+  const testCases = [0.015, 0.02, 0.0375];
+
+  testCases.forEach(maintenance => {
+    const params = createForecastParameters(maintenance);
+    expect(params.maintenancePercentage).toBe(maintenance);
+  });
+});