Why isn’t the global exception handler triggered in my C# unit test when a mocked exception is thrown?

I'm learning how to write unit tests for a C# API controller and want to ensure that my global exception handler is used when an exception occurs. I set up a mock to throw an exception, expecting the global handler (registered with the following code) to catch it and return a custom error object:

CSHARPCopied
builder.Services.AddExceptionHandler<MyGlobalExceptionHandler>();

However, when I run the unit test, the exception thrown by the mocked dependency bubbles up instead of being intercepted by the global error handler. Here’s the unit test:

CSHARPCopied
[Fact]
public async Task GetCustomerById_FailedByDbOps()
{
    // Arrange
    var customerId = 1;
    _customerRepoMock
        .Setup(repo => repo.GetOne(customerId))
        .ThrowsAsync(new Exception("Wrong or missing DB conn string"));

    // Act
    var result = await _controller.RetrieveCustomerById(customerId);

    // Assert
    var objResult = Assert.IsType<ObjectResult>(result);
    Assert.Equal(500, objResult.StatusCode);
}

The test fails by exposing the mock exception rather than triggering the global error handling logic. Why does this happen? Is there something wrong with my setup, or is it inherent to testing controllers directly (bypassing the ASP.NET Core pipeline where the exception handler is active)?

I appreciate any insights or alternative testing approaches that might help simulate the full middleware pipeline during testing.