Add ability to manage which websites can credit you in link previews (#31819)

spec/validators/lines_validator_spec.rb

@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe LinesValidator do
+  let(:record_class) do
+    Class.new do
+      include ActiveModel::Validations
+
+      attr_accessor :text
+
+      validates :text, lines: { maximum: 5 }
+    end
+  end
+
+  let(:record) { record_class.new }
+
+  describe '#validate_each' do
+    context 'with a nil value' do
+      it 'does not add errors' do
+        record.text = nil
+
+        expect(record).to be_valid
+        expect(record.errors).to be_empty
+      end
+    end
+
+    context 'with lines below the limit' do
+      it 'does not add errors' do
+        record.text = "hoge\n" * 5
+
+        expect(record).to be_valid
+        expect(record.errors).to be_empty
+      end
+    end
+
+    context 'with more lines than limit' do
+      it 'adds an error' do
+        record.text = "hoge\n" * 6
+
+        expect(record).to_not be_valid
+        expect(record.errors.where(:text)).to_not be_empty
+      end
+    end
+  end
+end