test: adding new test

src/__tests__/getDeviceOS.spec.ts

@@ -0,0 +1,27 @@
+import getDeviceOS from '../getDeviceOS';
+
+describe('validating src/getDeviceOS', () => {
+  let windowSpy: any;
+
+  beforeEach(() => {
+    windowSpy = jest.spyOn(window.navigator, 'userAgent', 'get');
+  });
+
+  afterEach(() => {
+    windowSpy.mockRestore();
+  });
+
+  it('should return `android` if got UA android', () => {
+    windowSpy.mockReturnValue(
+      'Mozilla/5.0 (Linux; Android 5.0; SM-G900P Build/LRX21T) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.88 Mobile Safari/537.36',
+    );
+    expect(getDeviceOS()).toBe('android');
+  });
+
+  it('should return `ios` if got UA ios', () => {
+    windowSpy.mockReturnValue(
+      'Mozilla/5.0 (iPhone; CPU iPhone OS 10_3_1 like Mac OS X) AppleWebKit/603.1.30 (KHTML, like Gecko) Version/10.0 Mobile/14E304 Safari/602.1',
+    );
+    expect(getDeviceOS()).toBe('ios');
+  });
+});

src/__tests__/isDarkmode.spec.ts

@@ -1,7 +1,7 @@
 import isDarkmode from '../isDarkmode';
 
 describe('validaing src/isDarkmode', () => {
-  let windowSpy;
+  let windowSpy: any;
 
   beforeEach(() => {
     windowSpy = jest.spyOn(window, 'window', 'get');