test: add weather logic test suite

tests/weather-utils.test.ts

@@ -0,0 +1,29 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  DEFAULT_WIND_SPEED_UNIT,
+  formatTemperature,
+  formatWindSpeed,
+  isTemperatureUnit,
+  isWindSpeedUnit,
+} from "@/lib/weather-utils";
+
+describe("weather utilities", () => {
+  it("formats wind speed in km/h by default", () => {
+    expect(DEFAULT_WIND_SPEED_UNIT).toBe("kmh");
+    expect(formatWindSpeed(5, "en")).toBe("18 km/h");
+  });
+
+  it("formats selected temperature and wind units", () => {
+    expect(formatTemperature(10, "en", "f")).toBe("50°F");
+    expect(formatWindSpeed(4, "en", "mph")).toBe("9 mph");
+    expect(formatWindSpeed(4, "en", "ms")).toBe("4.0 m/s");
+  });
+
+  it("validates supported presentation units", () => {
+    expect(isTemperatureUnit("c")).toBe(true);
+    expect(isTemperatureUnit("kelvin")).toBe(false);
+    expect(isWindSpeedUnit("kmh")).toBe(true);
+    expect(isWindSpeedUnit("knots")).toBe(false);
+  });
+});