def test_which_non_existing_app():
"""Test for a non existing app."""
assert utils.which('hypothetical_app') == None
def test_which_null_arg():
"""Test for a null string param (raises a ValueError)."""
utils.which('')
def test_which_existing_app():
"""Test for an existing app."""
assert utils.which('ls') == '/bin/ls' # Depends on your system