Adding some e-mail validation tests

frontend/src/utils/index.test.ts

-import { isValidMobilePhoneNumber } from './index'
+import { isValidEmail, isValidMobilePhoneNumber } from './index'
 
 // Mock i18next module to return a translation that just returns the key
 jest.mock('i18next', () => ({
@@ -12,3 +12,16 @@ test('Invalid phone number', async () => {
 test('Valid phone number', async () => {
   expect(isValidMobilePhoneNumber('+47 97510000')).toEqual(true)
 })
+
+test('Valid e-mail', async () => {
+  expect(isValidEmail('test@example.org')).toEqual(true)
+  expect(isValidEmail('Test.Tester@example.org')).toEqual(true)
+})
+
+test('Invalid e-mail', async () => {
+  expect(isValidEmail('testexample.org')).not.toEqual(true)
+  expect(isValidEmail('test')).not.toEqual(true)
+  // Treat special characters as invalid, some services allow them though
+  expect(isValidEmail('Øyvind.Åsen@example.org')).not.toEqual(true)
+  expect(isValidEmail('Test.Tester@åsen.org')).not.toEqual(true)
+})