Question:

When using git submodule update, an error is reported:

        fatal: Needed a single revision

        Unable to find current revision in submodule path 'test'

reason:

Git is incorrectly configured, or the code was downloaded from the sub module directory, but the association failed.

Solution:

        rm -rf test/

Then go back to the root directory of the main module and use the command again:

        git submodule update --init