Don't cast and extract normalization

We are not trying to handle user input so `cast` can be a no-op. Also
extract the base36 normalization logic, let the binary class handle the
serialize encoding and add some tests.

lib/rails_ext/active_record_uuid_type.rb

@@ -7,7 +7,11 @@ module ActiveRecord
       def self.generate
         uuid = SecureRandom.uuid_v7
         hex = uuid.delete("-")
-        hex.to_i(16).to_s(36).rjust(25, "0")
+        normalize_base36(hex.to_i(16))
+      end
+
+      def self.normalize_base36(integer)
+        integer.to_s(36).rjust(BASE36_LENGTH, "0")
       end
 
       def serialize(value)
@@ -15,19 +19,18 @@ module ActiveRecord
 
         hex = value.to_s.to_i(36).to_s(16).rjust(32, "0")
         binary = hex.scan(/../).map(&:hex).pack("C*")
-        binary.force_encoding(Encoding::BINARY)
-        Data.new(binary)
+        super(binary)
       end
 
       def deserialize(value)
         return unless value
 
         hex = value.to_s.unpack1("H*")
-        hex.to_i(16).to_s(36).rjust(BASE36_LENGTH, "0")
+        Uuid.normalize_base36(hex.to_i(16))
       end
 
       def cast(value)
-        deserialize(serialize(value))
+        value
       end
     end
   end

test/lib/rails_ext/active_record_uuid_type_test.rb

@@ -0,0 +1,50 @@
+require "test_helper"
+
+class ActiveRecordUuidTypeTest < ActiveSupport::TestCase
+  setup do
+    @type = ActiveRecord::Type::Uuid.new
+    @sample_uuid = "01jcqzx8h0000000000000000" # base36 UUID
+  end
+
+  test "cast nil returns nil" do
+    assert_nil @type.cast(nil)
+  end
+
+  test "cast returns value as-is" do
+    result = @type.cast(@sample_uuid)
+    assert_equal @sample_uuid, result
+  end
+
+  test "serialize returns binary Data object" do
+    result = @type.serialize(@sample_uuid)
+
+    assert_instance_of ActiveModel::Type::Binary::Data, result
+    assert_equal 16, result.to_s.bytesize
+    assert_equal Encoding::BINARY, result.to_s.encoding
+  end
+
+  test "serialize nil returns nil" do
+    assert_nil @type.serialize(nil)
+  end
+
+  test "deserialize converts binary to base36" do
+    binary_data = @type.serialize(@sample_uuid)
+
+    result = @type.deserialize(binary_data)
+
+    assert_equal @sample_uuid, result
+  end
+
+  test "deserialize handles raw binary string" do
+    binary_data = @type.serialize(@sample_uuid)
+    raw_binary = binary_data.to_s
+
+    result = @type.deserialize(raw_binary)
+
+    assert_equal @sample_uuid, result
+  end
+
+  test "deserialize nil returns nil" do
+    assert_nil @type.deserialize(nil)
+  end
+end