fix: address AI code-review findings (#78)

src/Wolfgang.Etl.TestKit.Xunit/ExtractorBaseContractTests.cs

@@ -29,7 +29,7 @@ namespace Wolfgang.Etl.TestKit.Xunit;
 ///   <item><description><c>CurrentItemCount</c> is incremented as items are yielded.</description></item>
 ///   <item><description><c>ReportingInterval</c> rejects values less than 1.</description></item>
 ///   <item><description><c>MaximumItemCount</c> stops extraction at the specified limit.</description></item>
-///   <item><description><c>MaximumItemCount</c> rejects values less than 0.</description></item>
+///   <item><description><c>MaximumItemCount</c> rejects values less than 1.</description></item>
 ///   <item><description><c>SkipItemCount</c> rejects values less than 0.</description></item>
 ///   <item><description>Progress callbacks fire at least once per extraction.</description></item>
 ///   <item><description><c>CreateProgressReport</c> reflects <c>CurrentItemCount</c>.</description></item>

src/Wolfgang.Etl.TestKit.Xunit/LoaderBaseContractTests.cs

@@ -30,7 +30,7 @@ namespace Wolfgang.Etl.TestKit.Xunit;
 ///   <item><description><c>CurrentItemCount</c> is incremented as items are loaded.</description></item>
 ///   <item><description><c>ReportingInterval</c> rejects values less than 1.</description></item>
 ///   <item><description><c>MaximumItemCount</c> stops loading at the specified limit.</description></item>
-///   <item><description><c>MaximumItemCount</c> rejects values less than 0.</description></item>
+///   <item><description><c>MaximumItemCount</c> rejects values less than 1.</description></item>
 ///   <item><description><c>SkipItemCount</c> skips the specified number of items.</description></item>
 ///   <item><description><c>SkipItemCount</c> rejects values less than 0.</description></item>
 ///   <item><description>Progress callbacks fire when the timer fires.</description></item>

src/Wolfgang.Etl.TestKit.Xunit/ManualProgressTimer.cs

@@ -31,9 +31,15 @@ namespace Wolfgang.Etl.TestKit.Xunit;
 /// TProgress? captured = null;
 /// var progress = new SynchronousProgress<TProgress>(r => captured = r);
 ///
-/// var task = sut.ExtractAsync(progress).ToListAsync().AsTask();
+/// // Begin enumeration and pull the first item so the pipeline is mid-flight,
+/// // then fire the timer deterministically before draining the rest. This
+/// // avoids the race where a fast synchronous source completes (and the
+/// // timer's Elapsed handler is unsubscribed in the worker's finally) before
+/// // Fire() is reached.
+/// await using var enumerator = sut.ExtractAsync(progress).GetAsyncEnumerator();
+/// await enumerator.MoveNextAsync();
 /// timer.Fire();
-/// await task;
+/// while (await enumerator.MoveNextAsync()) { }
 ///
 /// Assert.NotNull(captured);
 /// </code>

src/Wolfgang.Etl.TestKit.Xunit/TransformerBaseContractTests.cs

@@ -32,7 +32,7 @@ namespace Wolfgang.Etl.TestKit.Xunit;
 ///   <item><description><c>CurrentItemCount</c> is incremented as items are transformed.</description></item>
 ///   <item><description><c>ReportingInterval</c> rejects values less than 1.</description></item>
 ///   <item><description><c>MaximumItemCount</c> stops transformation at the specified limit.</description></item>
-///   <item><description><c>MaximumItemCount</c> rejects values less than 0.</description></item>
+///   <item><description><c>MaximumItemCount</c> rejects values less than 1.</description></item>
 ///   <item><description><c>SkipItemCount</c> skips the specified number of items.</description></item>
 ///   <item><description><c>SkipItemCount</c> rejects values less than 0.</description></item>
 ///   <item><description>Progress callbacks fire when the timer fires.</description></item>

src/Wolfgang.Etl.TestKit/TestExtractor.cs

@@ -186,6 +186,14 @@ [EnumeratorCancellation] CancellationToken token
     {
         token.ThrowIfCancellationRequested();
 
+        // The wrapped source is synchronous, so this iterator would otherwise
+        // contain no await. Yield once up front to honour the async-iterator
+        // contract on every exit path (including the MaximumItemCount
+        // yield-break) and to give callers an asynchronous hop. Placing it here
+        // rather than after the loop keeps it reachable regardless of how the
+        // loop terminates.
+        await Task.Yield();
+
         var enumerator     = (_enumerator ?? _enumerable!.GetEnumerator())!;
         var ownsEnumerator = _enumerator == null;
 
@@ -218,7 +226,5 @@ [EnumeratorCancellation] CancellationToken token
                 enumerator.Dispose();
             }
         }
-
-        await Task.Yield(); // satisfies async method contract without causing extra allocations
     }
 }