PhoneNumberField prefix tests miss 1-digit codes and the digits-only filter

[marassteiner]

Summary

PR #909 adds a free-text prefix field (1–3 digits, FilteringTextInputFormatter.digitsOnly, fixed + via prefixText). Widget tests cover 2-digit (43), 3-digit (423), empty-required, and the 4-digit cap. They do not cover:

• a 1-digit prefix (+1, +7)
• letters / mixed paste into the prefix field (the existing “digits-only” test writes only to the national-number field)
• pasting +41 into the prefix (double-plus) or deleting the decorative +

Found while reviewing #909. Not a merge-blocker: the formatters and the ^[0-9]{1,3}$ validator already encode those rules; this is a test-coverage gap on new logic.

Evidence

• lib/widgets/form/phone_number_field.dart:79 — FilteringTextInputFormatter.digitsOnly
• lib/widgets/form/phone_number_field.dart:91 — RegExp(r'^[0-9]{1,3}$')
• test/widgets/form/phone_number_field_test.dart:47,89 — _enterAndValidate / “digits-only” only call _numberField()
• test/widgets/form/phone_number_field_test.dart:138-145 — 2-digit prefix
• test/widgets/form/phone_number_field_test.dart:176-183 — 3-digit prefix
• test/widgets/form/phone_number_field_test.dart:199-206 — prefixText == '+' after typing 41, no paste/+ deletion case

Suggested follow-up

Add widget tests that:

1. Accept prefix 1 + a national number and compose +1….
2. Enter letters / mixed paste into _prefixField() and assert they are filtered or rejected.
3. Paste +41 and assert the stored value is still a single + plus digits.
4. Clear the editable prefix and assert the required-prefix error.

Related

• feat(kyc): open the phone country prefix field to any 1-3 digit dial code #909