Happy flow for creating realms works

But needs more validating...

IdentityShroud.Core.Tests/Fixtures/DbFixture.cs

@@ -0,0 +1,70 @@
+using DotNet.Testcontainers.Containers;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using Npgsql;
+using Testcontainers.PostgreSql;
+
+namespace IdentityShroud.Core.Tests.Fixtures;
+
+public class DbFixture : IAsyncLifetime
+{
+    private readonly IContainer _postgresqlServer;
+
+    private string ConnectionString =>
+                        $"Host={_postgresqlServer.Hostname};" +
+                        $"Port={DbPort};" +
+                        $"Username={Username};Password={Password}";
+
+    private string Username => "postgres";
+    private string Password => "password";
+    private string DbHostname => _postgresqlServer.Hostname;
+    private int DbPort => _postgresqlServer.GetMappedPublicPort(PostgreSqlBuilder.PostgreSqlPort);
+    
+    public Db CreateDbContext(string dbName)
+    {
+        var db = new Db(Options.Create<DbConfiguration>(new()
+        {
+            ConnectionString = ConnectionString + ";Database=" + dbName,
+            LogSensitiveData = false,
+        }), new NullLoggerFactory());
+        return db;
+    }    
+
+    public DbFixture()
+    {
+        _postgresqlServer = new PostgreSqlBuilder("postgres:18.1")
+            .WithName("KMS-Test-Infra-" + Guid.NewGuid().ToString("D"))
+            .WithPassword(Password)
+            .Build();
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        await _postgresqlServer.StopAsync();
+    }
+
+    public async ValueTask InitializeAsync()
+    {
+        await _postgresqlServer.StartAsync();
+    }
+
+    public NpgsqlConnection GetConnection(string dbname)
+    {
+        string connString = ConnectionString
+            + $";Database={dbname}";
+        var connection = new NpgsqlConnection(connString);
+        connection.Open();
+        return connection;
+    }
+}
+
+/*
+
+[CollectionDefinition("PostgresqlFixtureCollection", DisableParallelization = false)]
+public class PostgresqlFactoryCollection : ICollectionFixture<PostgresqlFixture>
+{
+    // This class has no code, and is never created. Its purpose is simply
+    // to be the place to apply [CollectionDefinition] and all the
+    // ICollectionFixture<> interfaces.
+}
+*/