Improve ValueDelegateAssertion failure messages if an exception was thrown in the delegate (#2522)

Author: thomhurst

TUnit.Assertions.Tests/ThrowInDelegateValueAssertionTests.cs

@@ -0,0 +1,28 @@
+using TUnit.Assertions.AssertConditions.Throws;
+
+namespace TUnit.Assertions.Tests;
+
+public class ThrowInDelegateValueAssertionTests
+{
+    [Test]
+    public async Task ThrowInDelegateValueAssertion_ReturnsExpectedErrorMessage()
+    {
+        var assertion = async () => await Assert.That(() =>
+        {
+            throw new Exception("No");
+            return true;
+        }).IsEqualTo(true);
+
+        await Assert.That(assertion)
+            .Throws<AssertionException>()
+            .WithMessageContaining("""
+                         Expected () =>
+                                 {
+                                     throw new Exception("No");
+                                     return true;
+                                 } to be equal to True
+
+                         but An exception was thrown during the assertion: System.Exception: No
+                         """);
+    }
+}

TUnit.Assertions/AssertConditions/ExpectedValueAssertCondition.cs

@@ -14,7 +14,7 @@ public void WithTransform(Func<TActual?, TActual?> actualTransformation,
     {
         _transformations.Add((actualTransformation, expectedTransformation));
     }
-    
+
     public void WithComparer(Func<TActual?, TExpected?, AssertionDecision> comparer)
     {
         _customComparers.Add(comparer);
@@ -26,13 +26,13 @@ AssertionMetadata assertionMetadata
     )
     {
         var expected = ExpectedValue;
-        
+
         foreach (var (actualTransformation, expectedTransformation) in _transformations)
         {
             actualValue = actualTransformation(actualValue);
             expected = expectedTransformation(expected);
         }
-        
+
         foreach (var result in _customComparers.Select(customComparer => customComparer(actualValue, expected)))
         {
             switch (result)
@@ -44,8 +44,13 @@ AssertionMetadata assertionMetadata
             }
         }
 
+        if (exception is not null)
+        {
+            return FailWithMessage($"An exception was thrown during the assertion: {exception}");
+        }
+
         return GetResult(actualValue, expected);
     }
-    
+
     protected abstract ValueTask<AssertionResult> GetResult(TActual? actualValue, TExpected? expectedValue);
-}
+}