Why am i getting 'uninitialized constant Mail::TestMailer' error with "Rails 6.1.5 & Ruby 3.1.0" while working without problems "Rails 6.1.5 & Ruby 3.0.1" ?
Found following from NEWS for Ruby 3.1.0.
The following default gems are now bundled gems.
net-ftp 0.1.3
net-imap 0.2.2
net-pop 0.1.1
net-smtp 0.3.1
matrix 0.4.2
prime 0.1.2
debug 1.4.0
So, i just added next 3 lines into GemFile. It worked fine.
gem 'net-smtp' # to send email
gem 'net-imap' # for rspec
gem 'net-pop' # for rspec