Q:

Running bazel build with an aspect on test targets does not yield test output jars

running bazel build //... \
--aspects some-aspect.bzl%some_aspect \
--output_groups=some_new_output,default
 does not create test jars outputs. 
on the other hand running bazel test does create the test jar outputs:
bazel test //... \
--aspects some-aspect.bzl%some_aspect \
--output_groups=some_new_output,default

How come?
This question was updated to reflect use of aspects:
The original question:

running bazel build //... does not add test code to output jar. 
on the other hand bazel test //... builds the test code but also
  runs it.
Is there a way in bazel to build the test code without running the
  tests?

A:

I had a mistake in the values I gave the --output_groups flag.
It should have been --output_groups=+some_new_output,+default
The default can even be omitted:
--output_groups=+some_new_output
This flag is not documented at all. There is an open issue on this in bazel github repo.

