SimpleCov issue. Some files not covered

SimpleCov ignore some files (0%) when others are successfully covered (100%) with the same tests.

I run my tests with the framework's testing tools (Rails 5.1.4).

This is my test_helper.rb file.

require 'simplecov'

# save to CircleCI's artifacts directory if we're on CircleCI
if ENV['CIRCLE_ARTIFACTS']
  dir = File.join(ENV['CIRCLE_ARTIFACTS'], 'coverage')
  SimpleCov.coverage_dir(dir)
end

SimpleCov.start 'rails'

ENV['RAILS_ENV'] ||= 'test'
require File.expand_path('../../config/environment', __FILE__)
require 'rails/test_help'

This is a file successfully covered (100%) by SimpleCov with a Connection.types :

class Connection < ApplicationRecord
  validates :type_of, inclusion: { in: proc { Connection.types.map(&:to_s) } }

  TYPES = %i[
    friend
    industry
    investor
  ].freeze

  belongs_to :project
  belongs_to :user

  def self.types
    TYPES
  end
end

This is a file unsuccessfully covered (0%) by SimpleCov with Kpi.types:

class Kpi < ApplicationRecord
  REGEX = {
    float: "^\d+(\.?\d)?$"
  }.freeze

  TYPES = [
    { id: :buyers, name: 'Number of buyers', unit: 'users', example: '1000', regex: :float },
    { id: :sellers, name: 'Number of sellers', unit: 'users', example: '1000', regex: :float },
  ].freeze

  belongs_to :project

  def self.types
    TYPES
  end
end

I don't see a pattern here... do you?

Ok, found the culprit: ActiveAdmin. Here is the answer for posterity :)

I added a filter:

SimpleCov.start 'rails' do
  add_filter('/admin')
end

And it works fine now.