I have a large python test file using unittest that I run from the command line.  Some tests take a while to run. This is a mild pain point because I'm often only concerned with the last test I added. What I want is this: 

add test. 
run tests  (one fails because I haven't written the code to make it pass)
implement the behaviour
run only the test that failed last time 
fix the silly error I made when implementing the code
run only the failing test, which passes this time
run all the tests to find out what I broke. 

Is it possible to do this from the command line?
Just run the test with --last-failed option (you might need pytest)
Python unittest, running only the tests that failed