diff --git a/spec/crypto_secret_spec.cr b/spec/crypto_secret_spec.cr
index 72f5072..ee47810 100644
--- a/spec/crypto_secret_spec.cr
+++ b/spec/crypto_secret_spec.cr
@@ -1,7 +1,8 @@
 require "./spec_helper"
+require "../src/crypto-secret/test"
+require "../src/crypto-secret/not"
+require "../src/crypto-secret/bidet"
+
+test_secret_class Crypto::Secret::Not
+test_secret_class Crypto::Secret::Bidet
 
-describe Crypto::Secret do
-  pending "works" do
-    false.should eq(true)
-  end
-end
diff --git a/src/crypto-secret/secret.cr b/src/crypto-secret/secret.cr
index fc48a23..f6b21c1 100644
--- a/src/crypto-secret/secret.cr
+++ b/src/crypto-secret/secret.cr
@@ -75,6 +75,17 @@ module Crypto::Secret
     io << self.class.to_s << "(***SECRET***)"
   end
 
+  def dup
+    readonly do |sslice|
+      obj = self.class.new sslice.bytesize
+      obj.readwrite do |dslice|
+        sslice.copy_to dslice
+      end
+      # TODO: copy state if possible
+      obj
+    end
+  end
+
   abstract def readwrite
   abstract def readonly
   abstract def noaccess
diff --git a/src/crypto-secret/test.cr b/src/crypto-secret/test.cr
new file mode 100644
index 0000000..6582319
--- /dev/null
+++ b/src/crypto-secret/test.cr
@@ -0,0 +1,78 @@
+macro test_secret_class(to sclass)
+  describe {{sclass}} do
+    sclass = {{sclass}}
+
+    it "returns a random secret" do
+      secret1 = sclass.new 8
+      secret2 = sclass.random 8
+      secret1.should_not eq secret2
+    end
+
+    it "copies & wipes on .move" do
+      ksize = 4
+      key1 = Bytes.new ksize
+      key1[1] = 1_u8
+      key2 = key1.dup
+      secret = sclass.move_from key2
+
+      secret.readonly { |s| s.should eq key1 }
+      key2.should eq Bytes.new(ksize)
+    end
+
+    it "copies & preserves on .copy" do
+      ksize = 2
+      key1 = Bytes.new ksize
+      key1[1] = 1_u8
+      key2 = key1.dup
+      secret = sclass.copy_from key2
+
+      secret.readonly { |s| s.should eq key1 }
+      key2.should eq key1
+    end
+
+    it "compares with ==" do
+      ksize = 32
+      key = Bytes.new ksize
+      key[1] = 1_u8
+
+      secret1 = sclass.copy_from key
+      secret1.readonly { |s| s.should eq key }
+
+      secret2 = sclass.copy_from key
+
+      (secret1 == secret2).should be_true
+      secret1.readonly do |s1|
+        secret2.readonly do |s2|
+          (s1 == s2).should be_true
+        end
+      end
+    end
+
+    it "dups" do
+      ksize = 2
+      key = Bytes.new ksize
+      key[1] = 1_u8
+
+      secret1 = sclass.copy_from key
+      secret2 = secret1.dup
+      (secret1 == secret2).should be_true
+    end
+
+    pending "check dup state" { }
+
+    it "bytesize" do
+      secret = sclass.new 5
+      secret.bytesize.should eq 5
+      secret.readonly { |s| s.bytesize.should eq 5 }
+    end
+
+    it "doesn't leak key material when inspecting" do
+      secret = sclass.new 5
+
+      secret.to_s.should_not match /Bytes|Slice|StaticArray/
+      secret.inspect.should_not match /Bytes|Slice|StaticArray/
+
+      secret.inspect.should match /\(\*\*\*SECRET\*\*\*\)$/
+    end
+  end
+end