Ao executar testes ou rake, se você vir:
WARNING: Nokogiri was built against LibXML version 2.9.0, but has dynamically loaded 2.7.8
Em seguida, faça o seguinte:
gem uninstall nokogiri libxml-ruby
brew update
brew uninstall libxml2
brew install libxml2 --with-xml2-config
brew uninstall libxslt
brew install libxslt
brew unlink libxslt
bundle config build.nokogiri -- --with-xml2-dir=/usr --with-xslt-dir=/usr --with-iconv-dir=/usr
bundle
Nokogiri agora deve ser compilado com a versão correta!