fix: WaitsFor not returning latest captured value

TUnit.Assertions.Tests/WaitsForAssertionTests.cs

@@ -380,6 +380,35 @@ public async Task WaitsFor_GitHub_Issue_Example_Scenario()
         }
     }
 
+    [Test]
+    public async Task WaitsFor_WithIsNotNull_ReturnsResolvedValue_Issue3623()
+    {
+        // Regression test for GitHub issue #3623
+        // WaitsFor was returning null instead of the resolved value when using IsNotNull()
+        TestEntity? currentValue = null;
+        var callCount = 0;
+
+        Func<TestEntity?> getEntity = () =>
+        {
+            callCount++;
+            if (callCount >= 3)
+            {
+                currentValue = new TestEntity { Id = 42, Name = "Resolved", IsReady = true };
+            }
+            return currentValue;
+        };
+
+        // This should wait until the entity is not null, then return the non-null entity
+        TestEntity? entity = await Assert.That(getEntity)
+            .WaitsFor(e => e.IsNotNull(), TimeSpan.FromSeconds(5));
+
+        // The bug was that entity would be null here, even though WaitsFor succeeded
+        await Assert.That(entity).IsNotNull();
+        await Assert.That(entity!.Id).IsEqualTo(42);
+        await Assert.That(entity.Name).IsEqualTo("Resolved");
+        await Assert.That(entity.IsReady).IsEqualTo(true);
+    }
+
     // Helper class for testing complex objects
     private class TestEntity
     {

TUnit.Assertions/Conditions/WaitsForAssertion.cs

@@ -57,8 +57,6 @@ protected override async Task<AssertionResult> CheckAsync(EvaluationMetadata<TVa
                 var assertion = _assertionBuilder(assertionSource);
                 await assertion.AssertAsync();
 
-                // Store the successfully resolved value so it can be returned
-                _resolvedValue = currentValue;
                 return AssertionResult.Passed;
             }
             catch (AssertionException ex)
@@ -92,12 +90,6 @@ protected override async Task<AssertionResult> CheckAsync(EvaluationMetadata<TVa
             $"assertion did not pass within {_timeout.TotalMilliseconds:F0}ms after {attemptCount} attempts. {lastErrorMessage}");
     }
 
-    /// <summary>
-    /// The resolved value after the assertion passes.
-    /// This allows users to capture and use the value in downstream assertions.
-    /// </summary>
-    private TValue? _resolvedValue;
-
     /// <summary>
     /// Executes the assertion and returns the resolved value upon success.
     /// This enables the pattern: Entity entity = await Assert.That(getEntity).WaitsFor(...);
@@ -107,8 +99,10 @@ protected override async Task<AssertionResult> CheckAsync(EvaluationMetadata<TVa
         // Execute the base assertion logic (which calls CheckAsync and handles the result)
         await base.AssertAsync();
 
-        // Return the resolved value that was stored when the assertion passed
-        return _resolvedValue;
+        // After CheckAsync succeeds, the context contains the updated value
+        // from the successful ReevaluateAsync call
+        var (value, _) = await Context.GetAsync();
+        return value;
     }
 
     protected override string GetExpectation() =>