stub not working

I am testing views. I dont understand why stubs are not working.
Can anyone help.

view code :

before(:all) do
    @current_user = stub("User")
    assigns[:message] = @current_user

       undefined method `stub' for #<RSpec::Cor

Mocks and stubs are not meant to be used in `before(:all)`. Mocks and
stubs are reset after every example; therefore, using them in
`before(:all)` does not make too much sense.

I suggest you switch to using `before(:each)` (or just `before` which
is the same thing). In general, use `before(:each)` and avoid
`before(:all)` unless you know exactly what you're doing. Tests that
bleed state or use global state are a big smell.