How to use @_implements in a get only property?

I tried to override SwiftUI.View.body and add some test code, so I'd like to try using @_implements to redirect "var body: some View" to a custom protocol, but it looks like @_implements doesn't support get only properties?

I can find @_implements in the Swift source code for functions, and for type alias, but not for get only properties.

@_implements itself doesn't report an error, but the compiler gives me this error.

protocol TestableView {
    associatedtype Body: View
    var body: Body { get }

struct TestView: View, TestableView { // Type 'TestView' does not conform to protocol 'View'
                                      // Type 'TestView' does not conform to protocol 'TestableView'
    @_implements(SwiftUI.View, body)
    var testBody: some View {

    @_implements(TestableView, body)
    var body: some View {