Fix URL scanning in note length validator and preview card fetching (#15827)

* Add tests

* Fix URL scanning in note length validator and preview card fetching

spec/services/fetch_link_card_service_spec.rb

@@ -77,6 +77,14 @@ RSpec.describe FetchLinkCardService, type: :service do
         expect(a_request(:get, 'http://example.com/test-')).to have_been_made.at_least_once
       end
     end
+
+    context do
+      let(:status) { Fabricate(:status, text: 'testhttp://example.com/sjis') }
+
+      it 'does not fetch URLs with not isolated from their surroundings' do
+        expect(a_request(:get, 'http://example.com/sjis')).to_not have_been_made
+      end
+    end
   end
 
   context 'in a remote status' do

spec/validators/note_length_validator_spec.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe NoteLengthValidator do
+  subject { NoteLengthValidator.new(attributes: { note: true }, maximum: 500) }
+
+  describe '#validate' do
+    it 'adds an error when text is over 500 characters' do
+      text = 'a' * 520
+      account = double(note: text, errors: double(add: nil))
+
+      subject.validate_each(account, 'note', text)
+      expect(account.errors).to have_received(:add)
+    end
+
+    it 'counts URLs as 23 characters flat' do
+      text   = ('a' * 476) + " http://#{'b' * 30}.com/example"
+      account = double(note: text, errors: double(add: nil))
+
+      subject.validate_each(account, 'note', text)
+      expect(account.errors).to_not have_received(:add)
+    end
+
+    it 'does not count non-autolinkable URLs as 23 characters flat' do
+      text   = ('a' * 476) + "http://#{'b' * 30}.com/example"
+      account = double(note: text, errors: double(add: nil))
+
+      subject.validate_each(account, 'note', text)
+      expect(account.errors).to have_received(:add)
+    end
+  end
+end