Add unit tests for isAndroid

src/isAndroid.js

@@ -1,3 +1 @@
-const userAgent = typeof navigator !== 'undefined' ? navigator.userAgent : ''
-
-export default () => /(android)/i.test(userAgent)
+export default () => /(android)/i.test(typeof navigator !== 'undefined' ? navigator.userAgent : '')

src/isAndroid.test.js

@@ -0,0 +1,32 @@
+import isAndroid from './isAndroid'
+
+const mockUserAgent = (userAgent) => {
+  Object.defineProperty(navigator, 'userAgent', { value: userAgent, writable: true })
+}
+
+const mockUndefinedNavigator = () => {
+  Object.defineProperty(global, 'navigator', { value: undefined, writable: true })
+}
+
+describe('isAndroid', () => {
+  test('returns false when navigator.userAgent does not contain android string', () => {
+    mockUserAgent('safari browser')
+    const result = isAndroid()
+
+    expect(result).toEqual(false)
+  })
+
+  test('returns true when navigator.userAgent contains android string', () => {
+    mockUserAgent('android browser')
+    const result = isAndroid()
+
+    expect(result).toEqual(true)
+  })
+
+  test('returns false when navigator is undefined', () => {
+    mockUndefinedNavigator()
+    const result = isAndroid()
+
+    expect(result).toEqual(false)
+  })
+})