Make partially shipped shipment able to be ready

Previously, all inventory units in a shipment needed to be on_hand or
cancelled in order for the shipment to be considered shippable.

This worked fine for most users, but it caused issues for users who were
partially shipping shipments manually using cartons.

This commit allows shipments with some shipped inventory units to still
be considered "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