Also test that new_user.avatar = old_user.avatar nils with a nil avatar.

test/integration_test.rb

@@ -199,12 +199,15 @@ class IntegrationTest < Test::Unit::TestCase
       assert_equal "5k.png", @dummy.avatar_file_name
     end
     
-    should "assign images from other Paperclips as well" do
+    context "that is assigned its file from another Paperclip attachment" do
+      setup do
         @dummy2 = Dummy.new
         @file2  = File.new(File.join(FIXTURES_DIR, "12k.png"))
         assert  @dummy2.avatar = @file2
         @dummy2.save
+      end
       
+      should "work when assigned a file" do
         assert_not_equal `identify -format "%wx%h" #{@dummy.avatar.to_file(:original).path}`,
                          `identify -format "%wx%h" #{@dummy2.avatar.to_file(:original).path}`
 
@@ -213,6 +216,18 @@ class IntegrationTest < Test::Unit::TestCase
         assert_equal `identify -format "%wx%h" #{@dummy.avatar.to_file(:original).path}`,
                      `identify -format "%wx%h" #{@dummy2.avatar.to_file(:original).path}`
       end
+      
+      should "work when assigned a nil file" do
+        @dummy2.avatar = nil
+        @dummy2.save
+
+        @dummy.avatar = @dummy2.avatar
+        @dummy.save
+        
+        assert !@dummy.avatar?
+      end
+    end    
+
   end
 
   if ENV['S3_TEST_BUCKET']