initialize a package.json
depend on mocha and chai
ignore node_modules
create a setup test
set test script
depend on express
depend on nodemon
create a hello world server
server static content
respond to button click
retrieve target value
post target to server
refactor shortening
refactor posting
create a shortener object
create a url repository
refactory InMemory repository
specifiy repository contract
refactor key generator
specify key generator