Use shared ArrayPoolMemoryAllocator in tests

tests/ImageSharp.Tests/Image/ImageFrameTests.cs

@@ -16,7 +16,8 @@ namespace SixLabors.ImageSharp.Tests
 
             private void LimitBufferCapacity(int bufferCapacityInBytes)
             {
-                var allocator = (ArrayPoolMemoryAllocator)this.configuration.MemoryAllocator;
+                var allocator = ArrayPoolMemoryAllocator.CreateDefault();
+                this.configuration.MemoryAllocator = allocator;
                 allocator.BufferCapacityInBytes = bufferCapacityInBytes;
             }
 

tests/ImageSharp.Tests/Image/ImageTests.cs

@@ -99,7 +99,8 @@ namespace SixLabors.ImageSharp.Tests
 
             private void LimitBufferCapacity(int bufferCapacityInBytes)
             {
-                var allocator = (ArrayPoolMemoryAllocator)this.configuration.MemoryAllocator;
+                var allocator = ArrayPoolMemoryAllocator.CreateDefault();
+                this.configuration.MemoryAllocator = allocator;
                 allocator.BufferCapacityInBytes = bufferCapacityInBytes;
             }
 

tests/ImageSharp.Tests/TestUtilities/ImageProviders/TestImageProvider.cs

@@ -21,11 +21,20 @@ namespace SixLabors.ImageSharp.Tests
     public abstract partial class TestImageProvider<TPixel> : ITestImageProvider, IXunitSerializable
         where TPixel : unmanaged, IPixel<TPixel>
     {
+        // Create a Configuration with Configuration.CreateDefaultInstance(),
+        // but use the shared MemoryAllocator from Configuration.Default.MemoryAllocator
+        private static Configuration CreateDefaultConfiguration()
+        {
+            var configuration = Configuration.CreateDefaultInstance();
+            configuration.MemoryAllocator = ImageSharp.Configuration.Default.MemoryAllocator;
+            return configuration;
+        }
+
         public PixelTypes PixelType { get; private set; } = typeof(TPixel).GetPixelType();
 
         public virtual string SourceFileOrDescription => string.Empty;
 
-        public Configuration Configuration { get; set; } = Configuration.CreateDefaultInstance();
+        public Configuration Configuration { get; set; } = CreateDefaultConfiguration();
 
         /// <summary>
         /// Gets the utility instance to provide information about the test image & manage input/output.

tests/ImageSharp.Tests/TestUtilities/TestImageExtensions.cs

@@ -663,7 +663,8 @@ namespace SixLabors.ImageSharp.Tests
             this TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            var allocator = (ArrayPoolMemoryAllocator)provider.Configuration.MemoryAllocator;
+            var allocator = ArrayPoolMemoryAllocator.CreateDefault();
+            provider.Configuration.MemoryAllocator = allocator;
             return new AllocatorBufferCapacityConfigurator(allocator, Unsafe.SizeOf<TPixel>());
         }