Make partially shipped shipment able to be ready

core/app/models/spree/shipment.rb

@@ -82,7 +82,7 @@ def can_transition_from_pending_to_shipped?
 
     def can_transition_from_pending_to_ready?
       order.can_ship? &&
-        inventory_units.all? { |iu| iu.allow_ship? || iu.canceled? } &&
+        inventory_units.all? { |iu| iu.shipped? || iu.allow_ship? || iu.canceled? } &&
         (order.paid? || !Spree::Config[:require_payment_to_ship])
     end
 

core/spec/models/spree/shipment_spec.rb

@@ -80,7 +80,7 @@
     end
 
     it 'returns pending if backordered' do
-      allow(shipment).to receive_messages inventory_units: [mock_model(Spree::InventoryUnit, allow_ship?: false, canceled?: false)]
+      allow(shipment).to receive_messages inventory_units: [mock_model(Spree::InventoryUnit, allow_ship?: false, canceled?: false, shipped?: false)]
       expect(shipment.determine_state(order)).to eq 'pending'
     end
 
@@ -300,7 +300,7 @@
         # Set as ready so we can test for change
         shipment.update_attributes!(state: 'ready')
 
-        allow(shipment).to receive_messages(inventory_units: [mock_model(Spree::InventoryUnit, allow_ship?: false, canceled?: false)])
+        allow(shipment).to receive_messages(inventory_units: [mock_model(Spree::InventoryUnit, allow_ship?: false, canceled?: false, shipped?: false)])
         expect(shipment).to receive(:update_columns).with(state: 'pending', updated_at: kind_of(Time))
         shipment.update_state
       end
@@ -865,4 +865,34 @@
       end
     end
   end
+
+  describe '#can_transition_from_pending_to_ready?' do
+    let(:shipment) { create(:shipment, order: order) }
+
+    subject { shipment.can_transition_from_pending_to_ready? }
+
+    context "with backordered inventory" do
+      before { shipment.inventory_units.update_all(state: "backordered") }
+
+      it "returns false" do
+        expect(subject).to be false
+      end
+    end
+
+    context "with on_hand inventory" do
+      before { shipment.inventory_units.update_all(state: "on_hand") }
+
+      it "returns true" do
+        expect(subject).to be true
+      end
+    end
+
+    context "with shipped inventory" do
+      before { shipment.inventory_units.update_all(state: "shipped") }
+
+      it "returns true" do
+        expect(subject).to be true
+      end
+    end
+  end
 end