Ensure that image_kind attribute is assigned first

... and test the other methods in the mixin

app/models/concerns/image_kind.rb

@@ -2,8 +2,20 @@ module ImageKind
   extend ActiveSupport::Concern
 
   included do
+    def assign_attributes(attributes)
+      # It's important that the image_kind attribute is assigned first, as it is intended to be used by
+      # carrierwave uploaders when they are mounted to work out which image versions to use.
+      image_kind = attributes.delete(:image_kind)
+      ordered_attributes = if image_kind.present?
+                             { image_kind:, **attributes }
+                           else
+                             attributes
+                           end
+      super ordered_attributes
+    end
+
     def image_kind
-      attributes.fetch(:image_kind, "default")
+      attributes.fetch("image_kind", "default")
     end
 
     def image_kind_config

test/unit/app/models/concerns/image_kind_test.rb

@@ -0,0 +1,34 @@
+require "test_helper"
+
+class ImageKindTest < ActiveSupport::TestCase
+  setup do
+    @test_instance = (
+      Class.new do
+        include ActiveModel::Model
+        include ActiveModel::Attributes
+        include ActiveModel::AttributeAssignment
+
+        include ImageKind
+
+        attr_reader :assigned_attributes
+
+        def assign_attributes(attributes)
+          @assigned_attributes = attributes
+        end
+      end
+    ).new
+  end
+
+  test "adds an image_kind method with a default" do
+    assert_equal "default", @test_instance.image_kind
+  end
+
+  test "reorders attributes so image_kind comes first" do
+    @test_instance.assign_attributes( file: "some file", image_kind: "some image kind")
+    assert_equal({ image_kind: "some image kind", file: "some file" }, @test_instance.assigned_attributes)
+  end
+
+  test "loads image_kind_config" do
+    assert_instance_of Whitehall::ImageKind, @test_instance.image_kind_config
+  end
+end