Broken Makefile

broken-makefile

.PHONY: clean install test test-tap test-api

clean: 
	rm ./test/results.tap

install:
	npm install

test:
	mocha -R list

test-tap:
	mocha -R tap > ./test/results.tap

test-api:
	NODE_ENV='test-api' node app.js &
	PID=$!
	mocha -R list ./test-api/rest-api.js
	kill $PID

output

$ make test-api
NODE_ENV='test-api' node app.js &
PID=
mocha -R list ./test-api/rest-api.js

kill ID
kill: illegal process id: ID
make: *** [test-api] Error 1