Add Phone Number Formatting Function

String/FormatPhoneNumber.test.js

@@ -0,0 +1,23 @@
+import { formatPhoneNumber } from './FormatPhoneNumber'
+
+describe('PhoneNumberFormatting', () => {
+  it('expects to return the formatted phone number', () => {
+    expect(formatPhoneNumber('1234567890')).toEqual('(123) 456-7890')
+  })
+
+  it('expects to return the formatted phone number', () => {
+    expect(formatPhoneNumber(1234567890)).toEqual('(123) 456-7890')
+  })
+
+  it('expects to throw a type error', () => {
+    expect(() => { formatPhoneNumber('1234567') }).toThrow('Invalid phone number.')
+  })
+
+  it('expects to throw a type error', () => {
+    expect(() => { formatPhoneNumber('123456text') }).toThrow('Invalid phone number.')
+  })
+
+  it('expects to throw a type error', () => {
+    expect(() => { formatPhoneNumber(12345) }).toThrow('Invalid phone number.')
+  })
+})