aspnetcore/test/WebSites/RazorPagesWebSite/HandlerTestPage.cshtml

@page "{handler?}"

@using RazorPagesWebSite

@functions{
    public string MethodName { get; set; }

    public IActionResult OnGet()
    {
        return Page();
    }

    public async Task<IActionResult> OnPostAsync()
    {
        await Task.CompletedTask;
        MethodName = nameof(OnPostAsync);
        return Page();
    }

    public async Task OnGetCustomer()
    {
        await Task.CompletedTask;
        MethodName = nameof(OnGetCustomer);
    }

    public async Task OnGetViewCustomerAsync()
    {
        await Task.CompletedTask;
        MethodName = nameof(OnGetViewCustomerAsync);
    }

    public async Task<CustomActionResult> OnPostCustomActionResult()
    {
        await Task.CompletedTask;
        return new CustomActionResult();
    }

    public CustomActionResult OnGetCustomACtionResultAsync()
    {
        return new CustomActionResult();
    }
}

Method: @MethodName
@using (Html.BeginForm())
{
    @Html.AntiForgeryToken()
}