Adding Ammonite REPL to Scala For Ad Hoc Testing

Ammonite is an interactive REPL for Scala, kind of like ipython is for Python.

I usually use IntelliJ IDE for Scala (which has a REPL and debugger among other things). Ammonite is great replacement though, when I don’t want to start up full blown IDE.

It’s really easy to get started with Ammonite. First it needs to be added to built.sbt file as a library dependency via:

libraryDependencies += "com.lihaoyi" % "ammonite" % "1.4.2" % "test" cross CrossVersion.full
Code language: JavaScript (javascript)

Warning: You may need to use an older version of ammonite based on your set up. I found 1.0.5 works better for some of my projects.

Warning 2: Make sure to remove “test” from version in build.sbt, if you are going to run it outside of test environment.

Once there, I just need to add the following lines of code to my file that I am trying to test:

ammonite.Main(
    predefCode = "println(\"Starting Debugging!\")"
).run(
    "test" -> myTestValue
)
Code language: JavaScript (javascript)

For example running a test for my test class above, via:

sbt "testOnly com.alexkras.AmmoniteTestClass"
Code language: CSS (css)

Will start the interactive REPL, where myTestValue will get exposed as a variable named test, allowing me to explore how test can be used.