diff --git a/stryker.conf.js b/stryker.conf.js
index 924c3bb..08c8b77 100644
--- a/stryker.conf.js
+++ b/stryker.conf.js
@@ -1,11 +1,16 @@
-module.exports = function(config) {
-  config.set({
-    mutator: "javascript",
-    packageManager: "yarn",
-    reporters: ["clear-text", "progress"],
-    testRunner: "command",
-    transpilers: [],
-    coverageAnalysis: "all",
-    mutate: ["index.js"]
+'use strict';
+
+module.exports = function cfg (config) {
+  config.set ({
+    mutator:          'javascript',
+    packageManager:   'yarn',
+    reporters:        [
+      'clear-text',
+      'progress'
+    ],
+    testRunner:       'command',
+    transpilers:      [],
+    coverageAnalysis: 'all',
+    mutate:           [ 'index.js' ]
   });
 };
diff --git a/test/encryption.js b/test/encryption.js
index 6a36b51..ce5f31c 100644
--- a/test/encryption.js
+++ b/test/encryption.js
@@ -20,7 +20,7 @@ test ('encryption 128', (t) => {
   const enc = crypto.encrypt_aes (
     'foo',
     'bar',
-    crypto.encryption_mode_cbc_128,
+    crypto.encryption_mode_cbc_128
   );
   t.is (typeof enc, 'string');
 });
@@ -29,12 +29,12 @@ test ('decryption 128', (t) => {
   const enc = crypto.encrypt_aes (
     'foo',
     'bar',
-    crypto.encryption_mode_cbc_128,
+    crypto.encryption_mode_cbc_128
   );
   const dec = crypto.decrypt_aes (
     enc,
     'bar',
-    crypto.encryption_mode_cbc_128,
+    crypto.encryption_mode_cbc_128
   );
   t.is (dec, 'foo');
 });
diff --git a/test/index.js b/test/index.js
index 4d5c8bb..a36d970 100644
--- a/test/index.js
+++ b/test/index.js
@@ -26,10 +26,10 @@ test ('random_hex should refuse lenght smaller 1', (t) => {
   const error = t.throws (
     () => (crypto.random_hex (0))
   );
-  t.is(error.message, 'invalid length');
+  t.is (error.message, 'invalid length');
 });
 
-test ('random_hex should always return correct length', (t)=>{
+test ('random_hex should always return correct length', (t) => {
   for (let i = 1; i < 32; i++) {
     const hex = crypto.random_hex (i);
     t.is (hex.length, i);
@@ -50,10 +50,10 @@ test ('random_string should refuse lenght smaller 1', (t) => {
   const error = t.throws (
     () => (crypto.random_string (0))
   );
-  t.is(error.message, 'invalid length');
+  t.is (error.message, 'invalid length');
 });
 
-test ('random_string should always return correct length', (t)=>{
+test ('random_string should always return correct length', (t) => {
   for (let i = 1; i < 32; i++) {
     const str = crypto.random_string (i);
     t.is (str.length, i);
diff --git a/test/index.js.save b/test/index.js.save
new file mode 100644
index 0000000..3e9a00d
--- /dev/null
+++ b/test/index.js.save
@@ -0,0 +1,136 @@
+/*
+ * Copyright (C) Sapphirecode - All Rights Reserved
+ * Created by Timo Hocker <timo@scode.ovh>, March 2020
+ */
+
+/* eslint-disable no-magic-numbers */
+// @ts-nocheck
+'use strict';
+
+const test = require ('ava');
+const crypto = require ('../index');
+
+test ('random_hex', (t) => {
+  const hex = crypto.random_hex (16);
+  t.is (hex.length, 16);
+  t.regex (hex, /^[0-9a-f]+$/iu);
+});
+
+test ('random_hex with default length', (t) => {
+  const hex = crypto.random_hex ();
+  t.is (hex.length, 8);
+  t.regex (hex, /^[0-9a-f]+$/iu);
+});
+
+test ('random_hex should refuse lenght smaller 1', (t) => {
+  const error = t.throws (
+    () => (crypto.random_hex (0))
+  );
+  t.is(error.message, 'invalid length');
+});
+
+test ('random_hex should always return correct length', (t)=>{
+  for (let i = 1; i < 32; i++) {
+    const hex = crypto.random_hex (i);
+    t.is (hex.length, i);
+  }
+});
+
+test ('random_string', (t) => {
+  const str = crypto.random_string (16);
+  t.is (str.length, 16);
+});
+
+test ('random_string with default length', (t) => {
+  const str = crypto.random_string ();
+  t.is (str.length, 8);
+});
+
+test ('random_string should refuse lenght smaller 1', (t) => {
+  const error = t.throws (
+    () => (crypto.random_string (0))
+  );
+  t.is(error.message, 'invalid length');
+});
+
+test ('random_string should always return correct length', (t)=>{
+  for (let i = 1; i < 32; i++) {
+    const str = crypto.random_string (i);
+    t.is (str.length, i);
+  }
+});
+
+
+test ('hash_sha512', (t) => {
+  const hash = crypto.hash_sha512 ('a', 'b');
+  t.is (
+    hash,
+    // eslint-disable-next-line max-len
+    '2d408a0717ec188158278a796c689044361dc6fdde28d6f04973b80896e1823975cdbf12eb63f9e0591328ee235d80e9b5bf1aa6a44f4617ff3caf6400eb172d'
+  );
+});
+
+test ('checksum', (t) => {
+  const hash = crypto.checksum ('foo');
+  t.is (
+    hash,
+    // eslint-disable-next-line max-len
+    '2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae'
+  );
+});
+
+test ('create_salt', (t) => {
+  const salt = crypto.create_salt ();
+  t.is (salt.length, 64);
+  t.regex (salt, /^[0-9a-f]+$/iu);
+});
+
+test ('sign_object', (t) => {
+  const obj = { foo: 'bar' };
+  t.notThrows (() => {
+    const str = crypto.sign_object (obj, 'baz');
+    t.is (typeof str, 'string');
+  });
+});
+
+test ('decode_signed', (t) => {
+  const obj = { foo: 'bar' };
+  const str = crypto.sign_object (obj, 'baz');
+  const dec = crypto.decode_signed (str);
+  t.deepEqual (obj, dec);
+});
+
+
+test ('reject tampered signatures', (t) => {
+  const obj = { foo: 'bar' };
+  const str = crypto.sign_object (obj, 'baz');
+  const dec = crypto.verify_signature (str, 'foo');
+  t.is (dec, null);
+});
+
+test ('reject old signatures', async (t) => {
+  const obj = { foo: 'bar' };
+  const str = crypto.sign_object (obj, 'baz');
+  await new Promise ((res) => {
+    setTimeout (res, 10);
+  });
+  const dec = crypto.verify_signature (str, 'baz', 1);
+  t.is (dec, null);
+});
+
+test ('do not reject valid signatures', async (t) => {
+  const obj = { foo: 'bar' };
+  const str = crypto.sign_object (obj, 'baz');
+  await new Promise ((res) => {
+    setTimeout (res, 10);
+  });
+  const dec = crypto.verify_signature (str, 'baz', 100);
+  t.deepEqual (obj, dec);
+});
+
+test ('decode problematic token', (t) => {
+  // eslint-disable-next-line max-len
+  const str = 'eyJpYXQiOjE1ODE0NDAwMTIyODgsIm9iaiI6eyJpZCI6MX19.24ZOsWrnfkNe%2FbM0r7DaVJMqE2bfn2aAM%2BZSzWeSf31OCTlXXNWD34RBL2X5v3UliYQ4IIsLNBFbaW9texPHug%3D%3D';
+  const obj = crypto.decode_signed (str);
+  t.deepEqual (obj, { id: 1 });
+});