models: require belong_to associations on geo_area

app/models/geo_area.rb

@@ -12,7 +12,7 @@
 #  geo_reference_id :string
 #
 class GeoArea < ApplicationRecord
-  belongs_to :champ
+  belongs_to :champ, optional: false
 
   store :properties, accessors: [
     :description,

spec/factories/geo_area.rb

@@ -1,5 +1,7 @@
 FactoryBot.define do
   factory :geo_area do
+    association :champ
+
     trait :cadastre do
       source { GeoArea.sources.fetch(:cadastre) }
       numero { '42' }

spec/models/geo_area_spec.rb

@@ -1,24 +1,24 @@
 RSpec.describe GeoArea, type: :model do
   describe '#area' do
-    let(:geo_area) { create(:geo_area, :polygon) }
+    let(:geo_area) { build(:geo_area, :polygon) }
 
     it { expect(geo_area.area).to eq(219.0) }
   end
 
   describe '#length' do
-    let(:geo_area) { create(:geo_area, :line_string) }
+    let(:geo_area) { build(:geo_area, :line_string) }
 
     it { expect(geo_area.length).to eq(30.8) }
   end
 
   describe '#location' do
-    let(:geo_area) { create(:geo_area, :point) }
+    let(:geo_area) { build(:geo_area, :point) }
 
     it { expect(geo_area.location).to eq("2°25'42\"N 46°32'19\"E") }
   end
 
   describe '#rgeo_geometry' do
-    let(:geo_area) { create(:geo_area, geometry: geometry) }
+    let(:geo_area) { build(:geo_area, geometry: geometry) }
 
     context 'invalid' do
       let(:geometry) do