fix: users for alias not balanced across threads (#90)

This is required due to the fact that, if tests are running with process or AppDomain isolation, all of the tests will enumerate through the users in the same order. 

Shuffling the enumerators is an approximation that saves having to find a way to synchronise between AppDomains or processes.

Author: ewingjm

bindings/src/Capgemini.PowerApps.SpecFlowBindings/Configuration/TestConfiguration.cs

@@ -4,6 +4,7 @@
     using System.Collections.Generic;
     using System.Configuration;
     using System.Linq;
+    using Capgemini.PowerApps.SpecFlowBindings.Extensions;
     using YamlDotNet.Serialization;
 
     /// <summary>
@@ -82,7 +83,7 @@ private Dictionary<string, IEnumerator<UserConfiguration>> UserEnumerators
                             .Distinct()
                             .ToDictionary(
                                 alias => alias,
-                                alias => this.Users.Where(u => u.Alias == alias).GetEnumerator());
+                                alias => this.GetUserEnumerator(alias));
                     }
                 }
 
@@ -119,7 +120,7 @@ public UserConfiguration GetUser(string userAlias, bool useCurrentUser = true)
                     var aliasEnumerator = this.UserEnumerators[userAlias];
                     if (!aliasEnumerator.MoveNext())
                     {
-                        this.UserEnumerators[userAlias] = this.Users.Where(u => u.Alias == userAlias).GetEnumerator();
+                        this.UserEnumerators[userAlias] = this.GetUserEnumerator(userAlias);
                         aliasEnumerator = this.UserEnumerators[userAlias];
                         aliasEnumerator.MoveNext();
                     }
@@ -149,5 +150,10 @@ internal void Flush()
         {
             CurrentUsers.Clear();
         }
+
+        private IEnumerator<UserConfiguration> GetUserEnumerator(string alias)
+        {
+            return this.Users.Where(u => u.Alias == alias).ToList().Shuffle().GetEnumerator();
+        }
     }
 }

bindings/src/Capgemini.PowerApps.SpecFlowBindings/Extensions/IListExtensions.cs

@@ -0,0 +1,35 @@
+namespace Capgemini.PowerApps.SpecFlowBindings.Extensions
+{
+    using System;
+    using System.Collections.Generic;
+
+    /// <summary>
+    /// Extensions for <see cref="IList{T}"/>.
+    /// </summary>
+    internal static class IListExtensions
+    {
+        private static readonly Random Rand = new Random();
+
+        /// <summary>
+        /// Randomises the order of a list.
+        /// </summary>
+        /// <typeparam name="T">The type of list items.</typeparam>
+        /// <param name="list">The list.</param>
+        /// <returns>The shuffled list.</returns>
+        internal static IList<T> Shuffle<T>(this IList<T> list)
+        {
+            var n = list.Count;
+
+            while (n > 1)
+            {
+                n--;
+                var k = Rand.Next(n + 1);
+                T value = list[k];
+                list[k] = list[n];
+                list[n] = value;
+            }
+
+            return list;
+        }
+    }
+}