The tests need to call a private method, Milvus uses `#define` to
replace private with public, the hack trick works but would be broken if
the including order changed.
This uses friend to make all things work well
Signed-off-by: yah01 <yang.cen@zilliz.com>
Signed-off-by: yah01 <yah2er0ne@outlook.com>
99e0f1e65a