Failing to run RSpec (uninitialized constant User (NameError) - ruby

Question

Trying to run bundle exec rspec spec/models/user_spec.rb but failing to execute (see error below).
Contents of user_spec.rb:
require 'rails_helper'
describe User do
pending "add some examples to (or delete) #{__FILE__}"
end
If I remove the last 3 lines, then it complete with 0 examples and 0 failures. However, when the last 3 lines are present, it generates an error
/spec/models/user_spec.rb:4:in `<top (required)>': uninitialized constant User (NameError)
from /var/lib/gems/1.9.1/gems/rspec-core-3.0.3/lib/rspec/core/configuration.rb:1057:in `load'
from /var/lib/gems/1.9.1/gems/rspec-core-3.0.3/lib/rspec/core/configuration.rb:1057:in `block in load_spec_files'
from /var/lib/gems/1.9.1/gems/rspec-core-3.0.3/lib/rspec/core/configuration.rb:1057:in `each'
from /var/lib/gems/1.9.1/gems/rspec-core-3.0.3/lib/rspec/core/configuration.rb:1057:in `load_spec_files'
from /var/lib/gems/1.9.1/gems/rspec-core-3.0.3/lib/rspec/core/runner.rb:97:in `setup'
from /var/lib/gems/1.9.1/gems/rspec-core-3.0.3/lib/rspec/core/runner.rb:85:in `run'
from /var/lib/gems/1.9.1/gems/rspec-core-3.0.3/lib/rspec/core/runner.rb:70:in `run'
from /var/lib/gems/1.9.1/gems/rspec-core-3.0.3/lib/rspec/core/runner.rb:38:in `invoke'
from /var/lib/gems/1.9.1/gems/rspec-core-3.0.3/exe/rspec:4:in `<top (required)>'
from /usr/local/bin/rspec:23:in `load'
from /usr/local/bin/rspec:23:in `<main>'
It seems it doesn't know what User is and treats it as a constant, when this is infact a model. I have verified in the ruby sandbox that I can create new Users in the database. Any ideas?
Answer:
After removing --warnings from .rspec (thank you kirti), current error was about capybara version being too low (requires 2.2). After installing the latest version (modifying gemfile and bundle install), rspec appears to be executing correctly. Thank you to all for your comments.

Answer 1

I had the same issue, this was due to rspec/rails_helper.rb not being called anywhere.
I added it to the .rspec file, so my file look like this
--color
--require spec_helper
--require rails_helper
This and adding warnings to false in the spec/spec_helper.rb solved it for me !
config.warnings = false

Answer 2

After removing --warnings from .rspec (thank you kirti), current error was about capybara version being too low (requires 2.2). After installing the latest version (modifying gemfile and bundle install), rspec appears to be executing correctly. Thank you to all for your comments.

Answer 3

For me, the issue was that the name of the class was not being correctly called due to it being in another namespace. For example, I had:
RSpec.describe User do
# ... some tests
end
where I should have had
RSpec.describe MyModule::User do
# ... some tests
end
because the user class was defined with the MyModule module.