When testing instance method in RSpec my empty array argument is not being read

Question

  describe "changes shopping array length" do
subject { described_class.new.change_array_length(group: [], num: 2) }
it "by responding to a method with arguments" do
  expect(subject).to respond_to(:change_array_length).with(2).arguments
end

This is what I have written so far. However, when I run the test I get:

Failure/Error:
   def change_array_length(group, num)
     group << num
   end
 
 ArgumentError:
   wrong number of arguments (given 1, expected 2)

I removed the num argument and the number of arguments goes down to 0 so it's not reading the empty array.

I've just started learning testing with a course using Ruby not RoR so let me know if I have this slightly wrong for testing the method with arguments!

Thanks!

Sampat Badhe · Accepted Answer · 2020-08-18 19:54:17Z

1

Based on expectation to verify respond_to, subject should be instance of described class not the the method call.

describe "changes shopping array length" do
  subject { described_class.new }
  it "by responding to a method with arguments" do
    expect(subject).to respond_to(:change_array_length).with(2).arguments
  end
end

Also one more thing based on your method definition, method does not seem to used named arguments, but when you are calling in subject you are passing as named arguments which @Aarthi mentioned in her answer.

answered Aug 18, 2020 at 19:54

Sampat Badhe

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2 Comments

Tigiras Over a year ago

Oh okay, so if I wanted to say check the group being passed into the method was empty... How would I test for that? Appreciate the help both of you =)

Sampat Badhe Over a year ago

@Tigiras relishapp.com/rspec/rspec-mocks/v/3-2/docs/setting-constraints/… This rspec doc will help you

Aarthi · Accepted Answer · 2020-08-18 16:59:42Z

0

subject { described_class.new.change_array_length([], 2) }

You used named arguments which will be considered as a hash(single argument). Pass like an unnamed argument as defined in the method.

answered Aug 18, 2020 at 16:59

Aarthi

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1 Comment

Tigiras Over a year ago

Hmm that doesn't seem to work. It now gives an error: Failure/Error: expect(subject).to respond_to(:change_array_length).with(2).arguments expected [2] to respond to :change_array_length with 2 arguments. The way I originally had it reads it as at least 1 argument?

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