test.bytecode_helper provides various utilities for sensibly testing bytecode generation. It isn't easy for CPython developers to discover, since it isn't documented and the file is mixed in with actual tests in the main test directory.

As discussed in #15494, it should be:

1. Moved from Lib/test/ to Lib/test/support (and imports in tests adjusted accordingly)
2. Documented in Doc/library/test.rst

This change only affects the default branch (since test.bytecode_helper is new in 3.4)