Check .dup state when Stateful

src/crypto-secret/lib.cr

@@ -1,4 +1,11 @@
 module Crypto
+  module Secret
+    module Stateless
+    end
+
+    module Stateful
+    end
+  end
 end
 
 require "crypto/subtle"

src/crypto-secret/stateful.cr

@@ -66,7 +66,9 @@ module Crypto::Secret
     end
 
     # WARNING: Not thread safe
-    private def set_state(new_state : State)
+    # Kept public for .dup
+    # :nodoc:
+    def set_state(new_state : State)
       return if @state == new_state
 
       case new_state

src/crypto-secret/test.cr

@@ -56,9 +56,11 @@ macro test_secret_class(to sclass)
       secret1 = sclass.copy_from key
       secret2 = secret1.dup
       (secret1 == secret2).should be_true
-    end
 
-    pending "check dup state" { }
+      if secret1.is_a?(Crypto::Secret::Stateful) && secret2.is_a?(Crypto::Secret::Stateful)
+        secret1.@state.should eq secret2.@state
+      end
+    end
 
     it "bytesize" do
       secret = sclass.new 5