add model level validation for uniqueness of step in a given workflow and version

app/models/workflow_step.rb

@@ -8,6 +8,7 @@ class WorkflowStep < ApplicationRecord
   validates :version, presence: true
   validates :repository, presence: true
   validates :status, inclusion: { in: %w[waiting completed queued error skipped] }
+  validates :process, uniqueness: { scope: %w[version workflow druid] }
 
   scope :lifecycle, -> { where.not(lifecycle: nil) }
   scope :incomplete, -> { where.not(status: %w[completed skipped]) }

spec/models/workflow_step_spec.rb

@@ -34,6 +34,20 @@
       expect(subject.valid?).to be false
     end
   end
+  context 'duplicate step for the same process/version' do
+    it 'is not valid if the step already exists for the same druid/workflow/version' do
+      dupe_step = described_class.new(
+        druid: subject.druid,
+        workflow: subject.workflow,
+        process: subject.process,
+        version: subject.version,
+        status: 'completed',
+        repository: 'dor'
+      )
+      expect(dupe_step.valid?).to be false
+      expect(dupe_step.errors.messages).to include(process: ['has already been taken'])
+    end
+  end
   describe '#as_milestone' do
     builder = {}
     before do

spec/requests/workflows/destroy_all_spec.rb

@@ -11,11 +11,12 @@
     let!(:item2) do
       FactoryBot.create(:workflow_step,
                         repository: 'sdr',
+                        process: 'publish',
                         druid: druid)
     end
 
     let!(:item3) do
-      FactoryBot.create(:workflow_step)
+      FactoryBot.create(:workflow_step, process: 'shelve')
     end
 
     let(:druid) { item1.druid }