After running npm test four node processes
keep on running:

85880  1  S        0:00,41 node node-sass/bin/node-sass --watch node-sass/test/fixtures/simple/tmp.scss
85883  1  S        0:00,41 node node-sass/bin/node-sass --watch --quiet node-sass/test/fixtures/simple/tmp.scss
85885  1  S        0:00,40 node node-sass/bin/node-sass --output-style compressed --watch node-sass/test/fixtures/simple/bar.scss
85888  1  S        0:00,42 node node-sass/bin/node-sass --output-style compressed --watch node-sass/test/fixtures/watching/index.scss

We need to explicitly kill them when the test is done.