add back test

Author: GarrettBeatty

sdk/test/Services/S3/UnitTests/Custom/MultipartDownloadManagerTests.cs

@@ -2283,6 +2283,44 @@ public async Task HttpSemaphore_RangeStrategy_HeldThroughProcessPartAsync()
 
         #region Semaphore Release Error Path Tests
 
+        [TestMethod]
+        public async Task StartDownloadAsync_WaitForCapacityFails_DoesNotReleaseHttpSemaphore()
+        {
+            // Arrange - Test that semaphore is NOT released when it was never acquired
+            var httpThrottler = new SemaphoreSlim(2, 2);
+            var initialCount = httpThrottler.CurrentCount;
+            
+            var mockDataHandler = new Mock<IPartDataHandler>();
+            
+            // WaitForCapacityAsync fails BEFORE HTTP semaphore is acquired
+            mockDataHandler
+                .Setup(x => x.WaitForCapacityAsync(It.IsAny<CancellationToken>()))
+                .ThrowsAsync(new InvalidOperationException("Simulated capacity wait failure"));
+            
+            var mockClient = MultipartDownloadTestHelpers.CreateMockS3Client();
+            var request = MultipartDownloadTestHelpers.CreateOpenStreamRequest();
+            var config = MultipartDownloadTestHelpers.CreateBufferedDownloadConfiguration();
+            var coordinator = new MultipartDownloadManager(
+                mockClient.Object, request, config, mockDataHandler.Object, null, httpThrottler);
+
+            // Act & Assert
+            try
+            {
+                await coordinator.StartDownloadAsync(null, CancellationToken.None);
+                Assert.Fail("Expected InvalidOperationException to be thrown");
+            }
+            catch (InvalidOperationException ex)
+            {
+                Assert.AreEqual("Simulated capacity wait failure", ex.Message);
+            }
+
+            // Assert - Semaphore should NOT be released (it was never acquired)
+            Assert.AreEqual(initialCount, httpThrottler.CurrentCount,
+                "HTTP semaphore should NOT be released when it was never acquired (failed before WaitAsync)");
+            
+            // Cleanup
+            httpThrottler.Dispose();
+        }
 
 
         [TestMethod]