diff --git a/test/utils.js b/test/utils.js
index 037254c..73bb9bb 100644
--- a/test/utils.js
+++ b/test/utils.js
@@ -1,9 +1,8 @@
 const fs = require('fs');
 const zlib = require('zlib');
+const { bytesToHex, concatBytes, hexToBytes } = require('../utils.js');
 const utf8ToBytes = (str) => new TextEncoder().encode(str);
-const hexToBytes = (str) => Uint8Array.from(Buffer.from(str, 'hex'));
 const truncate = (buf, length) => (length ? buf.slice(0, length) : buf);
-const bytesToHex = (buf) => Buffer.from(buf).toString('hex');
 
 const repeat = (buf, len) => {
   // too slow: Uint8Array.from({ length: len * buf.length }, (_, i) => buf[i % buf.length]);
@@ -12,18 +11,6 @@ const repeat = (buf, len) => {
   return out;
 };
 
-function concatBytes(...arrays) {
-  if (arrays.length === 1) return arrays[0];
-  const length = arrays.reduce((a, arr) => a + arr.length, 0);
-  const result = new Uint8Array(length);
-  for (let i = 0, pad = 0; i < arrays.length; i++) {
-    const arr = arrays[i];
-    result.set(arr, pad);
-    pad += arr.length;
-  }
-  return result;
-}
-
 // Everything except undefined, string, Uint8Array
 const TYPE_TEST_BASE = [
   null,
@@ -40,6 +27,7 @@ const TYPE_TEST_BASE = [
   new Int16Array([1, 2, 3]),
   new ArrayBuffer(100),
   new DataView(new ArrayBuffer(100)),
+  { constructor: { name: 'Uint8Array' }, length: '1e30' },
   () => {},
   async () => {},
   class Test {},
@@ -59,17 +47,15 @@ const TYPE_TEST_OPT = [
 
 const TYPE_TEST_NOT_BOOL = [false, true];
 const TYPE_TEST_NOT_BYTES = ['', 'test', '1', new Uint8Array([]), new Uint8Array([1, 2, 3])];
+const TYPE_TEST_NOT_STR = [' 1 2 3 4 5', '010203040x', 'abcdefgh', '1 2 3 4 5 ', 'bee', new String('1234')];
 const TYPE_TEST_NOT_INT = [-0.0, 0, 1];
 
 const TYPE_TEST = {
-  int: TYPE_TEST_BASE.concat(TYPE_TEST_NOT_BOOL).concat(TYPE_TEST_NOT_BYTES),
-  bytes: TYPE_TEST_BASE.concat(TYPE_TEST_NOT_INT).concat(TYPE_TEST_NOT_BOOL),
-  boolean: TYPE_TEST_BASE.concat(TYPE_TEST_NOT_INT).concat(TYPE_TEST_NOT_BYTES),
-  opts: TYPE_TEST_OPT,
-  hash: TYPE_TEST_BASE.concat(TYPE_TEST_NOT_BOOL)
-    .concat(TYPE_TEST_NOT_INT)
-    .concat(TYPE_TEST_NOT_BYTES)
-    .concat(TYPE_TEST_OPT),
+  int: TYPE_TEST_BASE.concat(TYPE_TEST_NOT_BOOL, TYPE_TEST_NOT_BYTES),
+  bytes: TYPE_TEST_BASE.concat(TYPE_TEST_NOT_INT, TYPE_TEST_NOT_BOOL),
+  boolean: TYPE_TEST_BASE.concat(TYPE_TEST_NOT_INT, TYPE_TEST_NOT_BYTES),
+  hex: TYPE_TEST_BASE.concat(TYPE_TEST_NOT_INT, TYPE_TEST_NOT_BOOL, TYPE_TEST_NOT_STR),
+  hash: TYPE_TEST_BASE.concat(TYPE_TEST_NOT_BOOL, TYPE_TEST_NOT_INT, TYPE_TEST_NOT_BYTES, TYPE_TEST_OPT),
 };
 
 function median(list) {
diff --git a/test/utils.test.js b/test/utils.test.js
index a66642f..2d4a50b 100644
--- a/test/utils.test.js
+++ b/test/utils.test.js
@@ -1,13 +1,28 @@
 const { deepStrictEqual, throws } = require('assert');
 const { describe, should } = require('micro-should');
-const utils = require('./utils.js');
+const { TYPE_TEST, unalign } = require('./utils.js');
+const utils = require('../utils.js');
 
 // Here goes test for tests...
 describe('Tests', () => {
-  should('Unalign', () => {
+  should('hexToBytes', () => {
+    for (let v of TYPE_TEST.hex) {
+      throws(() => {
+        utils.hexToBytes(v);
+      });
+    }
+  });
+  should('bytesToHex', () => {
+    for (let v of TYPE_TEST.bytes) {
+      throws(() => {
+        utils.bytesToHex(v);
+      });
+    }
+  });
+  should('unalign', () => {
     const arr = new Uint8Array([1, 2, 3]);
     for (let i = 0; i < 16; i++) {
-      const tmp = utils.unalign(arr, i);
+      const tmp = unalign(arr, i);
       deepStrictEqual(tmp, arr);
       deepStrictEqual(tmp.byteOffset, i);
       // check that it doesn't modify original