Trigger Command Upon File Changes

I've recently experimented with having tests triggered automatically whenever I change a particular file. I found this to significantly improve my workflow. Instead of making a code change and then hitting a shortcut (or typing a command) to run a unit test to verify that my code change did what it was supposed to do, the test runs automatically as soon as I press save in my editor.

I resisted the temptation of writing my own watcher using stat from GNU Coreutils and used inotify and entr. Both inotify and entr are so fast, even on large code bases, that I have them watch whole modules in my Java project.

The first watcher I used was inotify:

$ inotifywait -q -m -e close_write -r ~/src/foo/foo-server/src |
  while read -r file event; do
    clear
    time mvn -o -q  -f
    ~/src/foo/foo-server/pom.xml test -Dtest=XMLTest*
  done

It worked great and the only real downside was that it's Linux specific. entr on the other hand, runs on Linux, macOS, FreeBSD and OpenBSD alike. Moreover, its syntax is simpler than entr, so it has become my preferred file watcher:

$ find ~/src/foo/foo-server/src | 
  entr -c -p time mvn -o -q -f  ~/src/foo/foo-server/pom.xml test -Dtest=XMLTest*

Running a selected set of unit tests with Maven

While running this, I learned another thing: From before I knew that mvn can run a single test by using a #:

$ mvn test -Dtest=MyTestClass#oneTest`

But what if you want to run multiple tests or test classes? It's easy, you just add a comma:

$ mvn test -Dtest=MyTestClass,MyOtherTestClass`

As an added bonus mvn (or Surefire to be precise), support wildcards, so you can do:

$ mvn test -Dtest=My*

to run both MyTestClass and MyOtherTestClass. Clever, eh?

Happy coding!