Rails/Rspec - objects not existing until interacted with - ruby-on-rails

Question

I have the following code where I create some instances of records using FactoryBot:
describe "#force_recalculation_of_lab_container_labs" do
(1..5).each do |n|
let("lab_#{n}".to_sym) { create(:lab) }
let("lab_container_#{n}".to_sym) { create(:skill_path) }
let("lab_collection_#{n}".to_sym) do
create(:lab_collection, lab_container: eval("lab_container_#{n}"))
end
end
context 'when adding labs' do
it "starts with 0 labs" do
expect(lab_collection_1.labs.count).to eq(0)
end
(1..3).each do |n|
let("lab_collection_inclusion_#{n}") do
create(:lab_collection_inclusion,
included_item_id: eval("lab_#{n}").id,
included_item_type: 'Lab',
lab_collection_id: eval("lab_collection_1").id,
subscribed: 0)
end
end
it "updates the lab total correctly after adding labs" do
binding.pry
end
end
end
From my pry point, I receive the following:
LabCollectionInclusion.count
=> 0
lab_collection_1.lab_collection_inclusions.count
=> 0
When I then call a record individually, it appears to then exist:
lab_collection_inclusion_1
<LabCollectionInclusion:0x000055a45c985b10
id: 1,
included_item_id: 1,
included_item_type: "Lab",
lab_collection_id: 4,
subscribed: false,
created_at: Thu, 01 Nov 2018 10:48:00 UTC +00:00,
updated_at: Thu, 01 Nov 2018 10:48:00 UTC +00:00>
After which point it exists when searching:
LabCollectionInclusion.count
=> 1
lab_collection_1.lab_collection_inclusions.count
=> 1
Obviously I don't want to have to do this for every record so my 2 questions are first of all why is this happening, and second of all how to correct it?
Thanks in advance

Answer 1

This is expected behavior because let is designed to lazy-evaluated. Quote from the docs of let:
Note that let is lazy-evaluated: it is not evaluated until the first time the method it defines is invoked. You can use let! to force the method's invocation before each example.
As described in the documentation: Just let! (note the !) instead of let when you need the records to be created without calling them by their name first.