OccurredEvent ordering on monitored object is now done via thread-safe counter

Src/FluentAssertions/Events/EventMonitor.cs

@@ -30,6 +30,8 @@ public EventMonitor(object eventSource, Func<DateTime> utcNow)
 
         public T Subject => (T)subject.Target;
 
+        private EventRaisedOrder EventRaisedOrder { get; } = new();
+
         public EventMetadata[] MonitoredEvents
         {
             get
@@ -49,7 +51,7 @@ public OccurredEvent[] OccurredEvents
                     from eventName in recorderMap.Keys
                     let recording = GetRecordingFor(eventName)
                     from @event in recording
-                    orderby @event.TimestampUtc
+                    orderby @event.RaisedOrderIndex
                     select @event;
 
                 return query.ToArray();
@@ -125,7 +127,7 @@ private void AttachEventHandler(EventInfo eventInfo, Func<DateTime> utcNow)
         {
             if (!recorderMap.TryGetValue(eventInfo.Name, out _))
             {
-                var recorder = new EventRecorder(subject.Target, eventInfo.Name, utcNow);
+                var recorder = new EventRecorder(subject.Target, eventInfo.Name, utcNow, EventRaisedOrder);
                 if (recorderMap.TryAdd(eventInfo.Name, recorder))
                 {
                     recorder.Attach(subject, eventInfo);

Src/FluentAssertions/Events/EventRaisedOrder.cs

@@ -0,0 +1,20 @@
+using System.Threading;
+
+namespace FluentAssertions.Events
+{
+    /// <summary>
+    /// Tracks the order of events raised by <see cref="FluentAssertions.Events.EventMonitor{T}"/>.
+    /// </summary>
+    internal sealed class EventRaisedOrder
+    {
+        private int orderIndex = -1;
+
+        /// <summary>
+        /// Increments the current order index.
+        /// </summary>
+        public int Increment()
+        {
+            return Interlocked.Increment(ref orderIndex);
+        }
+    }
+}

Src/FluentAssertions/Events/EventRecorder.cs

@@ -25,11 +25,13 @@ internal sealed class EventRecorder : IEventRecording, IDisposable
         /// <param name="eventRaiser">The object events are recorded from</param>
         /// <param name="eventName">The name of the event that's recorded</param>
         /// <param name="utcNow">A delegate to get the current date and time in UTC format.</param>
-        public EventRecorder(object eventRaiser, string eventName, Func<DateTime> utcNow)
+        /// <param name="eventRaisedOrder">Class used to track order of raised events.</param>
+        public EventRecorder(object eventRaiser, string eventName, Func<DateTime> utcNow, EventRaisedOrder eventRaisedOrder)
         {
             this.utcNow = utcNow;
             EventObject = eventRaiser;
             EventName = eventName;
+            EventRaisedOrder = eventRaisedOrder;
         }
 
         /// <summary>
@@ -40,6 +42,8 @@ public EventRecorder(object eventRaiser, string eventName, Func<DateTime> utcNow
         /// <inheritdoc />
         public string EventName { get; }
 
+        private EventRaisedOrder EventRaisedOrder { get; }
+
         public Type EventHandlerType { get; private set; }
 
         public void Attach(WeakReference subject, EventInfo eventInfo)
@@ -77,7 +81,7 @@ public void RecordEvent(params object[] parameters)
         {
             lock (lockable)
             {
-                raisedEvents.Add(new RecordedEvent(utcNow(), parameters));
+                raisedEvents.Add(new RecordedEvent(utcNow(), EventRaisedOrder.Increment(), parameters));
             }
         }
 
@@ -105,7 +109,8 @@ public IEnumerator<OccurredEvent> GetEnumerator()
                 {
                     EventName = EventName,
                     Parameters = @event.Parameters,
-                    TimestampUtc = @event.TimestampUtc
+                    TimestampUtc = @event.TimestampUtc,
+                    RaisedOrderIndex = @event.RaisedOrderIndex
                 };
             }
         }

Src/FluentAssertions/Events/OccurredEvent.cs

@@ -21,5 +21,10 @@ public class OccurredEvent
         /// The exact date and time of the occurrence in <see cref="DateTimeKind.Local"/>.
         /// </summary>
         public DateTime TimestampUtc { get; set; }
+
+        /// <summary>
+        /// The order in which this event was raised on the monitored object.
+        /// </summary>
+        public int RaisedOrderIndex { get; set; }
     }
 }

Src/FluentAssertions/Events/RecordedEvent.cs

@@ -12,10 +12,11 @@ internal class RecordedEvent
         /// <summary>
         /// Default constructor stores the parameters the event was raised with
         /// </summary>
-        public RecordedEvent(DateTime utcNow, params object[] parameters)
+        public RecordedEvent(DateTime utcNow, int raisedOrderIndex, params object[] parameters)
         {
             Parameters = parameters;
             TimestampUtc = utcNow;
+            RaisedOrderIndex = raisedOrderIndex;
         }
 
         /// <summary>
@@ -27,5 +28,10 @@ public RecordedEvent(DateTime utcNow, params object[] parameters)
         /// Parameters for the event
         /// </summary>
         public object[] Parameters { get; }
+
+        /// <summary>
+        /// The order in which this event was invoked on the monitored object.
+        /// </summary>
+        public int RaisedOrderIndex { get; }
     }
 }

Tests/Approval.Tests/ApprovedApi/FluentAssertions/net47.verified.txt

@@ -1217,6 +1217,7 @@ namespace FluentAssertions.Events
         public OccurredEvent() { }
         public string EventName { get; set; }
         public object[] Parameters { get; set; }
+        public int RaisedOrderIndex { get; set; }
         public System.DateTime TimestampUtc { get; set; }
     }
 }

Tests/Approval.Tests/ApprovedApi/FluentAssertions/netcoreapp2.1.verified.txt

@@ -1217,6 +1217,7 @@ namespace FluentAssertions.Events
         public OccurredEvent() { }
         public string EventName { get; set; }
         public object[] Parameters { get; set; }
+        public int RaisedOrderIndex { get; set; }
         public System.DateTime TimestampUtc { get; set; }
     }
 }

Tests/Approval.Tests/ApprovedApi/FluentAssertions/netcoreapp3.0.verified.txt

@@ -1217,6 +1217,7 @@ namespace FluentAssertions.Events
         public OccurredEvent() { }
         public string EventName { get; set; }
         public object[] Parameters { get; set; }
+        public int RaisedOrderIndex { get; set; }
         public System.DateTime TimestampUtc { get; set; }
     }
 }

Tests/Approval.Tests/ApprovedApi/FluentAssertions/netstandard2.1.verified.txt

@@ -1217,6 +1217,7 @@ namespace FluentAssertions.Events
         public OccurredEvent() { }
         public string EventName { get; set; }
         public object[] Parameters { get; set; }
+        public int RaisedOrderIndex { get; set; }
         public System.DateTime TimestampUtc { get; set; }
     }
 }

Tests/FluentAssertions.Specs/Events/EventAssertionSpecs.cs

@@ -411,6 +411,28 @@ public void When_constraints_are_specified_it_should_filter_the_events_based_on_
                 .Which.PropertyName.Should().Be("Boo");
         }
 
+        [Fact]
+        public void When_events_are_raised_regardless_of_time_tick_it_should_return_by_invokation_order()
+        {
+            // Arrange
+            var observable = new TestEventRaisingInOrder();
+            var utcNow = 11.January(2022).At(12, 00).AsUtc();
+            using var monitor = observable.Monitor(() => utcNow);
+
+            // Act
+            observable.RaiseAllEvents();
+
+            // Assert
+            monitor.OccurredEvents[0].EventName.Should().Be(nameof(TestEventRaisingInOrder.InterfaceEvent));
+            monitor.OccurredEvents[0].RaisedOrderIndex.Should().Be(0);
+
+            monitor.OccurredEvents[1].EventName.Should().Be(nameof(TestEventRaisingInOrder.Interface2Event));
+            monitor.OccurredEvents[1].RaisedOrderIndex.Should().Be(1);
+
+            monitor.OccurredEvents[2].EventName.Should().Be(nameof(TestEventRaisingInOrder.Interface3Event));
+            monitor.OccurredEvents[2].RaisedOrderIndex.Should().Be(2);
+        }
+
         #endregion
 
         #region Should(Not)RaisePropertyChanged events
@@ -817,6 +839,22 @@ public void RaiseBothEvents()
             }
         }
 
+        private class TestEventRaisingInOrder : IEventRaisingInterface, IEventRaisingInterface2, IEventRaisingInterface3
+        {
+            public event EventHandler Interface3Event;
+
+            public event EventHandler Interface2Event;
+
+            public event EventHandler InterfaceEvent;
+
+            public void RaiseAllEvents()
+            {
+                InterfaceEvent?.Invoke(this, EventArgs.Empty);
+                Interface2Event?.Invoke(this, EventArgs.Empty);
+                Interface3Event?.Invoke(this, EventArgs.Empty);
+            }
+        }
+
         public interface IEventRaisingInterface
         {
             event EventHandler InterfaceEvent;
@@ -827,6 +865,11 @@ public interface IEventRaisingInterface2
             event EventHandler Interface2Event;
         }
 
+        public interface IEventRaisingInterface3
+        {
+            event EventHandler Interface3Event;
+        }
+
         public interface IInheritsEventRaisingInterface : IEventRaisingInterface
         {
         }

docs/_pages/releases.md

@@ -17,7 +17,7 @@ sidebar:
 * `ContainItemsAssignableTo` now expects at least one item assignable to `T` - [#1765](https://github.com/fluentassertions/fluentassertions/pull/1765)
 * Querying methods on classes, e.g. `typeof(MyController).Methods()`, now also includes static methods - [#1740](https://github.com/fluentassertions/fluentassertions/pull/1740)
 * Variable name is not captured after await assertion - [#1770](https://github.com/fluentassertions/fluentassertions/pull/1770)
-
+* `OccurredEvent` ordering on monitored object is now done via thread-safe counter - [#1723](https://github.com/fluentassertions/fluentassertions/pull/1773)
 ## 6.3.0
 
 ### What's New