test: throw exception when tenant id is missing for when using databa…

…se per tenant

src/MultiTenancyTests/using_database_per_tenant.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Threading.Tasks;
+using Marten;
+using Marten.Testing.Harness;
+using Shouldly;
+using Xunit.Abstractions;
+
+namespace MultiTenancyTests;
+
+public class using_database_per_tenant: IAsyncLifetime
+{
+    private readonly ITestOutputHelper _testOutputHelper;
+    private DocumentStore _theStore;
+
+    public using_database_per_tenant(
+        ITestOutputHelper testOutputHelper
+    ) => _testOutputHelper = testOutputHelper;
+
+    public async Task InitializeAsync()
+    {
+        _theStore = DocumentStore.For(
+            options =>
+            {
+                options.MultiTenantedWithSingleServer(ConnectionSource.ConnectionString);
+            }
+        );
+    }
+
+    [Fact]
+    public async Task should_not_meaning_ful_exception_when_tenant_id_is_missing()
+    {
+        Should.Throw<ArgumentNullException>(() => _theStore.LightweightSession());
+    }
+
+
+    public async Task DisposeAsync() => await _theStore.DisposeAsync();
+}