enforce event to topic map if the endpoint specifies

src/Tests/ApprovalFiles/APIApprovals.Approve.approved.txt

@@ -54,6 +54,7 @@ namespace NServiceBus
     {
         protected TopicTopology(NServiceBus.Transport.AzureServiceBus.TopologyOptions options, Microsoft.Extensions.Options.IValidateOptions<NServiceBus.Transport.AzureServiceBus.TopologyOptions> optionsValidator) { }
         public Microsoft.Extensions.Options.IValidateOptions<NServiceBus.Transport.AzureServiceBus.TopologyOptions> OptionsValidator { get; set; }
+        public bool ThrowIfUnmappedEventTypes { get; set; }
         public static NServiceBus.Transport.AzureServiceBus.TopicPerEventTopology Default { get; }
         protected abstract string GetPublishDestinationCore(string eventTypeFullName);
         public void Validate() { }
@@ -185,6 +186,7 @@ namespace NServiceBus.Transport.AzureServiceBus
         [NServiceBus.Transport.AzureServiceBus.AzureServiceBusTopics]
         [System.Text.Json.Serialization.JsonConverter(typeof(NServiceBus.Transport.AzureServiceBus.SubscribedEventToTopicsMapConverter))]
         public System.Collections.Generic.Dictionary<string, System.Collections.Generic.HashSet<string>> SubscribedEventToTopicsMap { get; init; }
+        public bool ThrowIfUnmappedEventTypes { get; set; }
     }
     public sealed class TopologyOptionsDisableValidationValidator : Microsoft.Extensions.Options.IValidateOptions<NServiceBus.Transport.AzureServiceBus.TopologyOptions>
     {
@@ -198,6 +200,7 @@ namespace NServiceBus.Transport.AzureServiceBus
     {
         public TopologyOptionsSerializationContext() { }
         public TopologyOptionsSerializationContext(System.Text.Json.JsonSerializerOptions options) { }
+        public System.Text.Json.Serialization.Metadata.JsonTypeInfo<bool> Boolean { get; }
         public System.Text.Json.Serialization.Metadata.JsonTypeInfo<System.Collections.Generic.Dictionary<string, System.Collections.Generic.HashSet<string>>> DictionaryStringHashSetString { get; }
         public System.Text.Json.Serialization.Metadata.JsonTypeInfo<System.Collections.Generic.Dictionary<string, string>> DictionaryStringString { get; }
         protected override System.Text.Json.JsonSerializerOptions? GeneratedSerializerOptions { get; }

src/Tests/EventRouting/TopicPerEventTopologyTests.cs

@@ -25,6 +25,18 @@ public void PublishDestination_Should_return_mapped_topic_when_event_is_mapped()
         Assert.That(result, Is.EqualTo("MyTopic"));
     }
 
+    [Test]
+    public void PublishDestination_Should_default_topic_to_event_name()
+    {
+        var topologyOptions = new TopologyOptions();
+
+        var topology = TopicTopology.FromOptions(topologyOptions);
+
+        var result = topology.GetPublishDestination(typeof(MyEvent));
+
+        Assert.That(result, Is.EqualTo(typeof(MyEvent).FullName));
+    }
+
     [Test]
     public void Should_self_validate()
     {
@@ -58,5 +70,16 @@ public void Should_allow_disabling_validation()
         Assert.DoesNotThrow(() => topology.Validate());
     }
 
+    [Test]
+    public void ThrowIfUnmappedEventTypes_Should_throw_when_type_unmapped()
+    {
+        var topologyOptions = new TopologyOptions();
+
+        var topology = TopicTopology.FromOptions(topologyOptions);
+        topology.ThrowIfUnmappedEventTypes = true;
+
+        Assert.Throws<System.Exception>(() => topology.GetPublishDestination(typeof(MyEvent)));
+    }
+
     class MyEvent;
 }

src/Transport/EventRouting/TopicPerEventTopology.cs

@@ -1,7 +1,6 @@
 namespace NServiceBus.Transport.AzureServiceBus;
 
 using System;
-using System.Collections.Generic;
 
 /// <summary>
 /// A topology that uses separate topic for each event.
@@ -105,7 +104,13 @@ public void OverrideSubscriptionNameFor(string queueName, string subscriptionNam
 
     /// <inheritdoc />
     protected override string GetPublishDestinationCore(string eventTypeFullName)
-        => Options.PublishedEventToTopicsMap.GetValueOrDefault(eventTypeFullName, eventTypeFullName);
+    {
+        if (!Options.PublishedEventToTopicsMap.TryGetValue(eventTypeFullName, out string? topic) && Options.ThrowIfUnmappedEventTypes)
+        {
+            throw new Exception($"Unmapped event type '{eventTypeFullName}'. All events must be mapped in `PublishedEventToTopicsMap` when `ThrowIfUnmappedEventTypes` is set");
+        }
+        return topic ?? eventTypeFullName;
+    }
 
     internal override SubscriptionManager CreateSubscriptionManager(
         SubscriptionManagerCreationOptions creationOptions) =>

src/Transport/EventRouting/TopicTopology.cs

@@ -28,6 +28,16 @@ protected TopicTopology(TopologyOptions options, IValidateOptions<TopologyOption
 
         internal TopologyOptions Options { get; }
 
+        /// <summary>
+        /// Determines if an exception should be thrown when attempting to publish an event not mapped in PublishedEventToTopicsMap
+        /// </summary>
+        public bool ThrowIfUnmappedEventTypes
+        {
+            get => Options.ThrowIfUnmappedEventTypes;
+            set => Options.ThrowIfUnmappedEventTypes = value;
+        }
+
+
         /// <summary>
         /// Creates an instance of the topology object based on serializable state.
         /// </summary>

src/Transport/EventRouting/TopologyOptions.cs

@@ -43,4 +43,9 @@ public Dictionary<string, string> QueueNameToSubscriptionNameMap
         get;
         init => field = value ?? [];
     } = [];
+
+    /// <summary>
+    /// Determines if an exception should be thrown when attempting to publish an event not mapped in PublishedEventToTopicsMap
+    /// </summary>
+    public bool ThrowIfUnmappedEventTypes { get; set; } = false;
 }