MONGOID-5269 Persist writing an attribute after a removal correctly (#5200)

* MONGOID-5269 Persist writing an attribute after a removal correctly

* change to save!

Author: neilshweky

lib/mongoid/attributes.rb

@@ -164,6 +164,11 @@ def write_attribute(name, value)
           else
             attributes[field_name] = typed_value
           end
+
+          # when writing an attribute, also remove it from the unsets,
+          # so that removing then writing doesn't result in a removal.
+          delayed_atomic_unsets.delete(field_name)
+
           typed_value
         end
       else

spec/mongoid/attributes_spec.rb

@@ -2214,4 +2214,19 @@
       end
     end
   end
+
+  context "when an attribute is removed then set" do
+    let(:cat) { Cat.create!(name: "Neil") }
+
+    before do
+      cat.remove_attribute("name")
+      cat.name = "Nissim"
+      cat.save!
+      cat.reload
+    end
+
+    it "correctly sets the attribute" do
+      expect(cat.name).to eq("Nissim")
+    end
+  end
 end