fix(core): make randomString deterministic and allow larger values (#2342)

Author: bernardobridge

packages/core/lib/runner.js

@@ -471,8 +471,17 @@ function $randomNumber(min, max) {
   return _.random(min, max);
 }
 
-function $randomString(length) {
-  return Math.random().toString(36).substr(2, length);
+function $randomString(length = 10) {
+  let s = '';
+  const alphabet =
+    'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
+  const alphabetLength = alphabet.length;
+
+  while (s.length < length) {
+    s += alphabet.charAt((Math.random() * alphabetLength) | 0);
+  }
+
+  return s;
 }
 
 function handleScriptHook(hook, script, hookEvents, contextVars = {}) {

packages/core/test/core/unit/context_functions.test.js

@@ -0,0 +1,30 @@
+const { test } = require('tap');
+const { contextFuncs } = require('../../../lib/runner');
+
+test('$randomString should return a string of the specified length', async function (t) {
+  const testStringOfLength = (length) => {
+    const defaultStringLength = 10;
+    const errors = [];
+    for (let i = 0; i < 10000; i++) {
+      const string = contextFuncs.$randomString(length);
+      if (string.length != (length || defaultStringLength)) {
+        errors.push(string);
+      }
+    }
+
+    t.ok(
+      errors.length == 0,
+      `All strings should be of length ${length || defaultStringLength}. Got ${
+        errors.length
+      } bad strings: ${JSON.stringify(errors)}`
+    );
+  };
+
+  //test with different size strings
+  testStringOfLength();
+  testStringOfLength(1);
+  testStringOfLength(2);
+  testStringOfLength(10);
+  testStringOfLength(100);
+  testStringOfLength(1000);
+});