undefined method `plain_specs' for # (NoMethodError)

Question

I have made a pull of a project that I have in my work and when I tried to run rails db:migrate, the terminal request to install \"Bundler 2\" so I do it.

Answer 1

It is a bug with bundler version 2.1.0.pre.2

I unistalled bundler gem and install different version of bundler gem

$ gem uninstall bundler
$ gem install bundler -v 2.0.2

It should work.