Added model test and created helper for E.164 phone format testing

test/helpers/phone_format_helper_test.rb

@@ -0,0 +1,37 @@
+module PhoneFormatHelperTest
+  # https://en.wikipedia.org/wiki/E.164
+  def assert_phone_format(contact)
+    contact.phone = '+.1'
+    assert contact.invalid?
+
+    contact.phone = '+123.'
+    assert contact.invalid?
+
+    contact.phone = '+1.123456789123456'
+    assert contact.invalid?
+
+    contact.phone = '+134.1234567891234'
+    assert contact.invalid?
+
+    contact.phone = '+000.1'
+    assert contact.invalid?
+
+    contact.phone = '+123.0'
+    assert contact.invalid?
+
+    contact.phone = '+1.2'
+    assert contact.valid?
+
+    contact.phone = '+123.4'
+    assert contact.valid?
+
+    contact.phone = '+1.12345678912345'
+    assert contact.valid?
+
+    contact.phone = '+134.123456789123'
+    assert contact.valid?
+
+    contact.phone = '+134.00000000'
+    assert contact.invalid?
+  end
+end