if w0 != 0 {
		t.Fatalf("write 1200 'x's: got %d writes, want 0", w0)
	}
	io.Copy(b0, onlyReader{strings.NewReader(strings.Repeat("x", 30))})
	if w0 != 0 {
		t.Fatalf("write 1230 'x's: got %d writes, want 0", w0)
	}
	io.Copy(b0, onlyReader{strings.NewReader(strings.Repeat("x", 9))})
	if w0 != 1 {
		t.Fatalf("write 1239 'x's: got %d writes, want 1", w0)
	}

	var w1 writeCountingDiscard

// type conversions. If so, then in the general case it writes
//
//	_cgoIndexNN := a
//	_cgoNN := &cgoIndexNN[i] // with type conversions, if any
//
// to sb, and writes
//
//	_cgoCheckPointer(_cgoNN, _cgoIndexNN)
//
// to sbCheck, and returns true. If a is a simple variable or field reference,
// it writes
//
//	_cgoIndexNN := &a
//