Rails date_select undefined method string - ruby-on-rails

Question

I need some help here,
I'm using the date_select helper from Rails in a form to get a date in the format %d/%m/%Y. The helper seems to work fine in development but it doesn't in test mode.
In test mode, I got failure/error when a failed POST is made and the test needs to re-render the view. I got the follow failure/error message:
Failure/Error: <%= f.date_select :birthdate,
ActionView::Template::Error:
undefined method `year' for "{3=>15, 2=>6, 1=>2001}":String
or, depending on how I format the date
ActionView::Template::Error:
undefined method `year' for "15/06/2001":String
It only happens with failed posts (when is needed to re-render the form), both for rspec request and feature tests. In development mode, it works fine to re-render de form.
My tests
# feature test
it "sign up with false credential" do
users = FactoryBot.attributes_for(:users)
visit 'users/sign_up'
fill_in 'user_name', :with => "test"
find_by_id('user_birthdate_3i').find("option[value='15']").select_option
find_by_id('user_birthdate_2i').find("option[value='6']").select_option
find_by_id('user_birthdate_1i').find("option[value='2001']").select_option
click_button('Save')
expect(page).to have_selector "#error_explanation"
end
And
# request test
it "signs usuario_candidato up with wrong attributes" do
users = FactoryBot.attributes_for(:users)
expect{ post user_registration_path,
:params => {
"user" => {
"name" => user[:name],
"birthdate" => "2018/12/31"
}
}
}.to change{ User.count }.by(0)
end
The form
<%= f.date_select :birthdate,
options = {
start_year: Date.current.year,
end_year: 1950,
order: [:day, :month, :year],
prompt: { day: 'day', month: 'month', year: 'year' }
}
%>
Some observations:
The same test format works for feature and request when the is a
successful post.
I'm using locale PT-BR, with default format to %d/%m/Y%
I'm using Postgres, with birthdate as Date type.
I'm using Devise controller to this form, and I didn't override the controller's actions.
As I already said, development mode don't reproduce this error.
I already try different date format (e.g %m/%d%/%Y or year/month/day) before posting, it always return the same error. Because of that, my suggestion to the problem is: after the post fails, the return is a String when it should be a Date class.
Anyone already face this problem?
Any additional information, just ask on comments.
Thanks in advance!
UPDATE
After 6 days of posting, I was trying a suggestion someone gave on comments, and it happens that the tests passed, no error was raised. I didn't make the suggestion, I just change from a text_field to the date_field (as I wasn't able to use date_field, I changed to text_field and moved on to the next problem).
I found a certain inconsistency at how Rails works with date. Before the first raise of the problem, it was passing the tests normally. Then the error happened, now it's not happen anymore.
I have similar problem with a Regex that I use in my model for validate dates:
Model
# dd/mm/yyyy
VALID_DATE = /\A[0-9]{2}\/[0-9]{2}\/[0-9]{4}\z/
validates :birthdate, presence: true, format: { with: VALID_DATE, message: "must be in the format DD/MM/YYYY" }
When I create the validation, it works fine. Values in the format yyyy-mm-dd used not pass in model tests. In the next day, Rspec started to raise errors saying that yyyy-mm-dd and others should be valid (therefore, ignoring the regex validation)
Model test error
User birthdate should be invalid
Failure/Error: expect(user).to_not be_valid
expected #<User id: nil, name: "Sra. Margarida Sophie Santana", birthdate: "2000-12-29", created_at: nil, updated_at: nil> not to be valid
The only thing I have extra for date is a date_formats.rb in config/initializer with the follow value:
Date::DATE_FORMATS[:default] = "%d/%m/%Y"
I have it for a long time.
Apparently Rails changes when it decides to transform string values in date values (when it was passing the regex validation test, it was passing the date as string, when the problem raise up the date was been transformed from string to date before the validation).