diff --git a/packages/contracts/contracts/Entropy.sol b/packages/contracts/contracts/Entropy.sol
index c192eb8..47c6948 100644
--- a/packages/contracts/contracts/Entropy.sol
+++ b/packages/contracts/contracts/Entropy.sol
@@ -65,7 +65,7 @@ contract EntropyNFT is ERC721, Ownable {
             );
             result = operateOr(result, tokenIds[i]);
         }
-        _mint(msg.sender, result);
+        _safeMint(msg.sender, result);
     }
 
     function tokenURI(uint256 tokenId)
diff --git a/packages/contracts/test/entropy.js b/packages/contracts/test/entropy.js
index 60b0ad5..e7cddeb 100644
--- a/packages/contracts/test/entropy.js
+++ b/packages/contracts/test/entropy.js
@@ -18,7 +18,38 @@ contract('Entropy', (accounts) => {
     assert.equal("http://localhost:3000/token/0x0000000000000400.json", tokenUri);
   })
 
-  it('can convert token ids to hex', async function () {
-    assert.equal(1 == 2)
+  it('can mint new  tokens ids', async function () {
+    const receipt = await entropy.mintWithTokens(["2251799813685248", "72057594037927936"]);
+    const logs = receipt.logs[0];
+    assert.equal(logs.event, "Transfer");
+    const newTokenId = logs.args.tokenId;
+    assert.equal("74309393851613184", newTokenId.toString());
+
+    const tokenUri = await entropy.tokenURI("74309393851613184");
+    assert.equal(tokenUri, "http://localhost:3000/token/0x0108000000000000.json")
   })
+
+  it('can mint many tokens', async function () {
+    const tokenIdx = [10, 20, 30, 40, 50, 60, 42, 17, 32, 8];
+    const _ids = tokenIdx.map(async (idx) => {
+      const tokenId = await entropy.tokenByIndex(idx)
+      return tokenId.toString()
+    })
+
+    const ids = await Promise.all(_ids);
+
+    const firstResult = await entropy.mintWithTokens(ids.slice(0, 5));
+    const secondResult = await entropy.mintWithTokens(ids.slice(5));
+
+    const firstNewToken = firstResult.logs[0].args.tokenId.toString();
+    const secondNewToken = secondResult.logs[0].args.tokenId.toString();
+
+    const combinedRes = await entropy.mintWithTokens([firstNewToken, secondNewToken]);
+    const combinedId = combinedRes.logs[0].args.tokenId.toString();
+    const combinedUri = await entropy.tokenURI(combinedId);
+    assert.equal(combinedId, "2308105813808514304")
+    assert.equal(combinedUri, "http://localhost:3000/token/0x20080a0240120500.json");
+
+  })
+
 });