Rspec inconsistent results between 2 tests with same code - ruby-on-rails

Question

I have a model spec that throws an unexpected error (doesn't build the object right).
When I move the same code into a previous test, it runs smoothly.
Here's the problematic expectation:
expect(title.full_title.length).to be <= 140
When adding the line to the first test, it passes, while the second test fails:
describe "generates a title" do
let(:collection) { FactoryBot.create(:collection) }
let(:items) { FactoryBot.create_list(:item, 10, collection: collection, chosen: true) }
let(:title) { Title.create_title(collection) }
context "happy path" do
it "assigns keywords by score" do
array = []
items.each do |i|
array << [i.search.term, i.search.score]
end
array.sort! { |a, b| a[1] <=> b[1] }
split_title = title.full_title.split(', ')
remaining_chars = 140
i = 0
split_title.each do |s|
if remaining_chars - s.length >= 0
expect(s).to eq(array[i][0])
i += 1
remaining_chars -= s.length
end
expect(title.full_title.length).to be <= 140
end
end
it "does not exceed 140 characters" do
expect(title.full_title.length).to be <= 140
end
end
Here is the error message, it doesn't create the object:
1) Title generates a title happy path does not exceed 140 characters
Failure/Error: remaining_chars = 140 - keywords[0].length
NoMethodError:
undefined method `length' for nil:NilClass
TIA!

Answer 1

This is a long shot, but let's try if I'm lucky today.
Guess: Title.full_title implementation (which you didn't share) depends somehow on the existence of the Item's related to the collection which is used to initialize the Title object.
If that assumption is correct, different behavior comes from the lazy nature of let.
In the first it, you actually call items (e.g. items.each) so the let(:items) is evaluated, the rows in DB are created and title.full_title does not return nil.
There a few possible many ways to fix it:
Improve the implementation of full_title to always return string.
call items before in the second scenario
it "does not exceed 140 characters" do
items
expect(title.full_title.length).to be <= 140
end
use let!(:items) which is evaluated immediately (not lazy)