How to use (- Hyphen) in a variable name in shell?

Assuming an environment variable, since test-ing is not a valid shell variable name, you can use printenv:

% env foo-bar=baz printenv foo-bar
baz

Or Perl:

% env foo-bar=baz perl -e 'print $ENV{"foo-bar"}'
baz

Or other tools like Python, etc.

In the rc shell or derivatives (es, akanga), just about anything can be used in a variable name.

All variables are also exported to the environment.

However, in Byron Rakitzis' clone of rc for Unix (from which es/akanga derive), as opposed to the port of plan9 rc (now publicly available since plan9 has been released as FLOSS), note that for those that contain characters outside of a-zA-Z0-9_ or sequences of two or more underscores, an encoding/decoding is used upon export/import from the environment:

$ rc
; foo-bar = baz
; echo $'foo-bar'
baz
; printenv foo-bar
; env | grep foo
foo__2dbar=baz

In Byron's rc, one also can't use a variable with an empty name:

; '' = 1
rc: zero-length variable name

Things like 1 = foo or * = (foo bar) work, but they set the positional parameters, not variables.