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used the wrong method in a test

Co-Authored-By: Olle Jonsson <[email protected]>

spec/discard/model_spec.rb

@@ -42,7 +42,7 @@
       end
 
       it "should be kept?" do
-        expect(post).to be_undiscarded
+        expect(post).to be_kept
       end
 
       describe '#discard' do