rspec test fails code in rails controller - ruby-on-rails

Question

In my application_controller.rb, i have a line of code as follows:
def index
CaseStatus.order(:application_source).pluck(:application_source).uniq!
end
In my rspec code, i have a line of code that visits the index path of application_controller as follows
visit applications_path
When i run the code directly, it works perfectly but when it visits application_controller.rb via rspec, i get an error which says
NoMethodError:
undefined method `compact' for nil:NilClass
Not sure while i get this error via rspec and capybara but if i run the code as
def index
CaseStatus.order(:application_source).pluck(:application_source)
end
It executes perfectly with no errors. Kinda confused what the uniq! breaks in the code that suddenly the result becomes nil.
i get this error
Failure/Error: #application_channels = CaseStatus.order(:application_source).pluck(:application_source).uniq!.compact if CaseStatus.order(:application_source).present?
NoMethodError:
undefined method `compact' for nil:NilClass
# ./app/controllers/loan_applications_controller.rb:53:in `index'

Answer 1

I do not think uniq! is the method you would like to use in this case, see:
Returns nil if no changes are made (that is, no duplicates are found).
https://ruby-doc.org/core-2.2.0/Array.html#method-i-uniq-21
So it works like this:
2.3.1 :008 > a = [1,2,3,3,nil].uniq!
=> [1, 2, 3, nil]
2.3.1 :009 > a = [1,2,3,nil].uniq!
=> nil
2.3.1 :010 >
on the other hand uniq works like:
2.3.1 :010 > a = [1,2,3,3,nil].uniq
=> [1, 2, 3, nil]
2.3.1 :011 > a = [1,2,3,nil].uniq
=> [1, 2, 3, nil]
and on the output of uniq it is safe to run compact to remove nil values.