Adds a user spam integration test.

This is mainly to test server load as well as SQLite async support.

tests/Tgstation.Server.Tests/IntegrationTest.cs

@@ -142,6 +142,7 @@ namespace Tgstation.Server.Tests
 						await Assert.ThrowsExceptionAsync<UnauthorizedException>(() => badClient.Version(cancellationToken)).ConfigureAwait(false);
 
 						await new AdministrationTest(adminClient.Administration).Run(cancellationToken).ConfigureAwait(false);
+						await new UsersTest(adminClient.Users).Run(cancellationToken).ConfigureAwait(false);
 						await new InstanceManagerTest(adminClient.Instances, server.Directory).Run(cancellationToken).ConfigureAwait(false);
 					}
 				}

tests/Tgstation.Server.Tests/UsersTest.cs

@@ -0,0 +1,60 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Tgstation.Server.Api.Models;
+using Tgstation.Server.Client;
+
+namespace Tgstation.Server.Tests
+{
+	sealed class UsersTest
+	{
+		readonly IUsersClient client;
+
+		public UsersTest(IUsersClient client)
+		{
+			this.client = client ?? throw new ArgumentNullException(nameof(client));
+		}
+
+		public async Task Run(CancellationToken cancellationToken)
+		{
+			await TestSpamCreation(cancellationToken).ConfigureAwait(false);
+		}
+
+		public async Task TestSpamCreation(CancellationToken cancellationToken)
+		{
+			ICollection<Task<User>> tasks = new List<Task<User>>();
+
+			// Careful with this, very easy to overload the thread pool
+			const int RepeatCount = 100;
+
+			ThreadPool.GetMaxThreads(out var defaultMaxWorker, out var defaultMaxCompletion);
+			ThreadPool.GetMinThreads(out var defaultMinWorker, out var defaultMinCompletion);
+			try
+			{
+				ThreadPool.SetMinThreads(Math.Min(RepeatCount * 4, defaultMaxWorker), Math.Min(RepeatCount * 4, defaultMaxCompletion));
+				for (int i = 0; i < RepeatCount; ++i)
+				{
+					tasks.Add(
+						client.Create(
+							new UserUpdate
+							{
+								Name = $"SpamTestUser_{i}",
+								Password = "asdfasdjfhauwiehruiy273894234jhndjkwh"
+							},
+							cancellationToken));
+				}
+
+				await Task.WhenAll(tasks).ConfigureAwait(false);
+			}
+			finally
+			{
+				ThreadPool.SetMinThreads(defaultMinWorker, defaultMinCompletion);
+			}
+
+			Assert.AreEqual(RepeatCount, tasks.Select(task => task.Result.Id).Distinct().Count(), "Did not receive expected number of unique user IDs!");
+		}
+	}
+}