Fix sanitizer making block level elements unreadable (#10836)

Fix #10834

spec/lib/sanitize_config_spec.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+require Rails.root.join('app', 'lib', 'sanitize_config.rb')
+
+describe Sanitize::Config do
+  describe '::MASTODON_STRICT' do
+    subject { Sanitize::Config::MASTODON_STRICT }
+
+    it 'converts h1 to p' do
+      expect(Sanitize.fragment('<h1>Foo</h1>', subject)).to eq '<p>Foo</p>'
+    end
+
+    it 'converts ul to p' do
+      expect(Sanitize.fragment('<p>Check out:</p><ul><li>Foo</li><li>Bar</li></ul>', subject)).to eq '<p>Check out:</p><p>Foo<br>Bar</p>'
+    end
+
+    it 'converts p inside ul' do
+      expect(Sanitize.fragment('<ul><li><p>Foo</p><p>Bar</p></li><li>Baz</li></ul>', subject)).to eq '<p>Foo<br>Bar<br>Baz</p>'
+    end
+
+    it 'converts ul inside ul' do
+      expect(Sanitize.fragment('<ul><li>Foo</li><li><ul><li>Bar</li><li>Baz</li></ul></li></ul>', subject)).to eq '<p>Foo<br>Bar<br>Baz</p>'
+    end
+  end
+end