Xcode – Best Practice for testing Managed Buffers?

In my experience, there is no best practice to test code when it comes to rendering api’s, since there are many different factors here:
GPU and CPU vendors (Apple, AMD, Intel), operating systems, drivers.

I agree with Jeshua:

The best practice for testing hardware compatibility is on the actual
hardware in which you are testing compatibility.

There are many useful ways that can make development and testing easier:

You can detect vendors id:

id<MTLDevice> device = MTLCreateSystemDefaultDevice();
NSString* appleGPU = [device.name containsString:@"Apple"];
NSString* intelGPU = [device.name containsString:@"Intel"];
NSString* amdGPU = [device.name containsString:@"AMD"];
NSString* nvidiaGPU = [device.name containsString:@"Nvidia"];

With following method you can find your gpu type:

bool externalGPU = [device isRemovable] == true;
bool integratedGPU = [device isLowPower] == true;
bool discreteGPU = [device isLowPower] == false;

Note:

[device isLowPower];

On a Mac with an Apple silicon M1 chip, the property is NO because the
GPU runs with both high performance and low power.

Determine TBDR GPU architecture:

if (@available(macOS 10.15, *)) {
    if ([device supportsFamily: MTLGPUFamilyApple4])
    {
        // The GPU does support Tile-Based Deferred Rendering technique
    }
}

Understand the Managed Mode:

In a unified memory model, a resource with a MTLStorageModeManaged
mode resides in system memory accessible to both the CPU and the GPU.

Behaves like MTLStorageModeShared, has only one copy of content.

Note:

In a unified memory model, Metal may ignore
synchronization calls completely because it only creates a single
memory allocation for the resource.

You can also check some implementations by other developers:

PixarAnimationStudios/USD:

HgiMetalCapabilities::HgiMetalCapabilities(id<MTLDevice> device)
{
    if (@available(macOS 10.14.5, ios 12.0, *)) {
        _SetFlag(HgiDeviceCapabilitiesBitsConcurrentDispatch, true);
    }

    defaultStorageMode = MTLResourceStorageModeShared;
    bool unifiedMemory = false;
    if (@available(macOS 100.100, ios 12.0, *)) {
        unifiedMemory = true;
    } else if (@available(macOS 10.15, ios 13.0, *)) {
#if defined(ARCH_OS_IOS) || (defined(__MAC_10_15) && __MAC_OS_X_VERSION_MAX_ALLOWED >= __MAC_10_15)
        unifiedMemory = [device hasUnifiedMemory];
#else
        unifiedMemory = [device isLowPower];
#endif
    }

    _SetFlag(HgiDeviceCapabilitiesBitsUnifiedMemory, unifiedMemory);

#if defined(ARCH_OS_MACOS)
    if (!unifiedMemory) {
        defaultStorageMode = MTLResourceStorageModeManaged;
    }
#endif
}

KhronosGroup/MoltenVK

// Metal Managed:
//  - applies to both buffers and textures
//  - default mode for textures on macOS
//  - two copies of each buffer or texture when discrete memory available
//  - convenience of shared mode, performance of private mode
//  - on unified systems behaves like shared memory and has only one copy of content
//  - when writing, use:
//      - buffer didModifyRange:
//      - texture replaceRegion:
//  - when reading, use:
//      - encoder synchronizeResource: followed by
//      - cmdbuff waitUntilCompleted (or completion handler)
//      - buffer/texture getBytes: