Check name contains at least one letter

We have a claim on production with a surname of ".", we want to ensure
that the claimant's name includes at least one letter!

app/models/name_format_validator.rb

@@ -1,10 +1,11 @@
 class NameFormatValidator < ActiveModel::EachValidator
   NAME_REGEX_FILTER = /\A[^\[\]\^"=$%#&*+\/\\()@?!<>_`|{}~0-9]*\z/
+  HAS_LETTERS_FILTER = /[a-zA-Z]/
 
   def validate_each(record, attribute, value)
     return unless value.present?
 
-    unless NAME_REGEX_FILTER.match?(value)
+    unless NAME_REGEX_FILTER.match?(value) && HAS_LETTERS_FILTER.match?(value)
       record.errors.add(attribute, options[:message])
     end
   end

spec/forms/personal_details_form_spec.rb

@@ -271,6 +271,7 @@
       it { should validate_length_of(:first_name).is_at_most(100).with_message("First name must be less than 100 characters") }
       it { should_not allow_value("*").for(:first_name).with_message("First name cannot contain special characters") }
       it { should allow_value("O'Brian").for(:first_name) }
+      it { should_not allow_value(".").for(:first_name) }
 
       it { should validate_length_of(:middle_name).is_at_most(61).with_message("Middle names must be less than 61 characters") }
       it { should_not allow_value("&").for(:middle_name).with_message("Middle names cannot contain special characters") }
@@ -280,6 +281,7 @@
       it { should validate_length_of(:surname).is_at_most(100).with_message("Last name must be less than 100 characters") }
       it { should_not allow_value("$").for(:surname).with_message("Last name cannot contain special characters") }
       it { should allow_value("O'Brian").for(:surname) }
+      it { should_not allow_value(".").for(:surname) }
 
       it { should validate_presence_of(:national_insurance_number).with_message("Enter a National Insurance number in the correct format") }
       it { should allow_value("QQ123456C").for(:national_insurance_number) }