Trying to run rspec, but it couldn't read the tests file - ruby-on-rails

Question

require 'rails_helper'
RSpec.describe User, type: :model do
before { #user = FactoryGirl.build(:user) }
it { expect(#user).to respond_to(:email) }
end
The error:
/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:10: warning: constant Gem::ConfigMap is deprecated
/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:10: warning: constant Gem::ConfigMap is deprecated
/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:29: warning: constant Gem::ConfigMap is deprecated
/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:30: warning: constant Gem::ConfigMap is deprecated
/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:10: warning: constant Gem::ConfigMap is deprecated
WARN: Unresolved or ambiguous specs during Gem::Specification.reset:
diff-lcs (< 2.0, >= 1.2.0)
/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:10: warning: constant Gem::ConfigMap is deprecated
Available/installed versions of this gem:
- 1.5.0
- 1.3
WARN: Clearing out unresolved specs. Try 'gem cleanup <gem>'
Please report a bug if this causes problems.
/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:10: warning: constant Gem::ConfigMap is deprecated
/var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/formatters.rb:212:in `require': cannot load such file -- rspec/core/formatters/progress_formatter (LoadError)
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/formatters.rb:212:in `built_in_formatter'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/formatters.rb:182:in `find_formatter'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/formatters.rb:152:in `add'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/formatters.rb:127:in `setup_default'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/reporter.rb:47:in `block in prepare_default'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/reporter.rb:236:in `ensure_listeners_ready'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/reporter.rb:207:in `notify'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/reporter.rb:100:in `message'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/world.rb:196:in `report_filter_message'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/world.rb:188:in `announce_filters'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/runner.rb:104:in `ensure in setup'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/runner.rb:104:in `setup'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/runner.rb:86:in `run'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/runner.rb:71:in `run'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/lib/rspec/core/runner.rb:45:in `invoke'
from /var/lib/gems/2.3.0/gems/rspec-core-3.9.3/exe/rspec:4:in `<top (required)>'
from /usr/local/bin/rspec:23:in `load'
from /usr/local/bin/rspec:23:in `<main>'

Answer 1

First, we need to remove the unnecessary gem. Try running bundle clean --force.
This command will remove all unused gems in your bundler directory. This is useful when you have made many changes to your gem dependencies.
You can check more information about that comment in this link.
Now runs
bundle install
and try to rerun your tests. It seems that those two steps have helped other people:
https://github.com/rubygems/rubygems/issues/1945#issuecomment-334979982