Add shared specs for AtomicInternalId concern.

app/models/concerns/atomic_internal_id.rb

@@ -26,7 +26,7 @@ module AtomicInternalId
 
   included do
     class << self
-      def has_internal_id(on, scope:, usage: nil, init: nil) # rubocop:disable Naming/PredicateName
+      def has_internal_id(on, scope:, usage: nil, init:) # rubocop:disable Naming/PredicateName
         before_validation(on: :create) do
           if self.public_send(on).blank? # rubocop:disable GitlabSecurity/PublicSend
 

spec/models/issue_spec.rb

@@ -9,11 +9,17 @@ describe Issue do
   describe 'modules' do
     subject { described_class }
 
-    it { is_expected.to include_module(InternalId) }
     it { is_expected.to include_module(Issuable) }
     it { is_expected.to include_module(Referable) }
     it { is_expected.to include_module(Sortable) }
     it { is_expected.to include_module(Taskable) }
+
+    it_behaves_like 'AtomicInternalId' do
+      let(:internal_id_attribute) { :iid }
+      let(:instance) { build(:issue) }
+      let(:scope_attrs) { { project: instance.project } }
+      let(:usage) { :issues }
+    end
   end
 
   subject { create(:issue) }

spec/support/shared_examples/models/atomic_internal_id_spec.rb

+require 'spec_helper'
+
+shared_examples_for 'AtomicInternalId' do
+  describe '.has_internal_id' do
+    describe 'Module inclusion' do
+      subject { described_class }
+
+      it { is_expected.to include_module(AtomicInternalId) }
+    end
+
+    describe 'Validation' do
+      subject { instance }
+
+      before do
+        allow(InternalId).to receive(:generate_next).and_return(nil)
+      end
+
+      it { is_expected.to validate_presence_of(internal_id_attribute) }
+      it { is_expected.to validate_numericality_of(internal_id_attribute) }
+    end
+
+    describe 'internal id generation' do
+      subject { instance.save! }
+
+      it 'calls InternalId.generate_next and sets internal id attribute' do
+        iid = rand(1..1000)
+        expect(InternalId).to receive(:generate_next).with(instance, scope_attrs, usage, any_args).and_return(iid)
+        subject
+        expect(instance.public_send(internal_id_attribute)).to eq(iid) # rubocop:disable GitlabSecurity/PublicSend
+      end
+
+      it 'does not overwrite an existing internal id' do
+        instance.public_send("#{internal_id_attribute}=", 4711) # rubocop:disable GitlabSecurity/PublicSend
+        expect { subject }.not_to change { instance.public_send(internal_id_attribute) } # rubocop:disable GitlabSecurity/PublicSend
+      end
+    end
+  end
+end