fix test for hdkey cache

test/hdkeys.js

@@ -76,11 +76,6 @@ describe('BIP32 compliance', function() {
     publicKey.toString().should.equal(publicKey.xpubkey);
   });
 
-  it('cache for xpubkey works for test vector 1', function() {
-    var pk = HDPrivateKey(vector1_m_private);
-    pk.xpubkey.should.equal(pk.xpubkey);
-  });
-
   it('should get the extended public key from the extended private key for test vector 1', function() {
     HDPrivateKey(vector1_m_private).xpubkey.should.equal(vector1_m_public);
   });

test/hdprivatekey.js

@@ -100,6 +100,14 @@ describe('HDPrivate key interface', function() {
       testnetKey.publicKey.network.should.equal(Networks.testnet);
       livenetKey.publicKey.network.should.equal(Networks.livenet);
     });
+
+    it('cache for xpubkey works', function() {
+      var privateKey = new HDPrivateKey(xprivkey);
+      should.not.exist(privateKey._hdPublicKey);
+      privateKey.xpubkey.should.equal(privateKey.xpubkey);
+      should.exist(privateKey._hdPublicKey);
+    });
+
   });
 
   it('inspect() displays correctly', function() {