Coming Up for Air

Kotlin+Micronaut and IDEA Don't Get Along Together

Friday, January 25, 2019 |

Recently, I’ve been experimenting with Micronaut, a new-ish "modern, JVM-based, full-stack framework for building modular, easily testable microservice and serverless applications" from the makers of Grail. So far, I’ve been really impressed. The documentation has been excellent, and the framework is very easy to get started with. I have, though, run in to some trouble writing tests, or, more accurately running tests. I spent far too much time trying to figure it out until I finally broke down and asked, and it turns out that it’s IDEA’s fault. While that’s a bit annoying, there is a workaround, which I’d like to document briefly here.

If you read the getting started guide for Micronaut, you’ll notice a section on setting up your IDE. Having grown accustomed to having my projects "just work" in an IDE thanks to the excellent support for Maven and Gradle build files, I was a bit taken aback by this, but it turns out that Micronaut uses annotation processing fairly heavily, so you just have to tell IDEA to do the same when using its internal build system:

intellij annotation processors

If you’re using Java or Groovy, you’re all set. If you’re using Kotlin, however, you’re not. As the bug linked above points out, Kotlin’s kapt tool is not working correctly with IDEA’s internal build system. You have a couple of options, then. You can run your tests from the command line, using either Maven or Gradle, or you can change the test configuration to execute the build using the external tool before running or debugging your test.

For example, I created a brand new (demo) application, then added a controller:

$ mn create-app -l kotlin -b maven --features=junit demo
|Generating Kotlin project...
|Application created at C:\Users\jdlee\src\micronaut\demo
$ cd demo
$ mn create-controller Author
|Rendered template Controller.kt to destination src\main\kotlin\demo\AuthorController.kt
|Rendered template to destination src\test\java\demo\

From IDEA, if I Run AuthorControllerTest, the test will fail with a very unhelpful message:

C:\java\jdk8\bin\java.exe ...
13:15:35.686 [main] INFO  i.m.context.env.DefaultEnvironment - Established active environments: [test]
13:15:35.700 [main] INFO  i.m.context.env.DefaultEnvironment - Established active environments: [test]

io.micronaut.http.client.exceptions.HttpClientResponseException: Page Not Found

The trick is to change how IDEA builds the project before starting the test. With the AuthorControllerTest configuration created for us by virtue of having just tried to run the test, we just need to edit that configuration and change the "Before Launch" steps.

This is how it should look by default:

micronaut default test config

We want to click plus icon and tell it to run a Maven goal (or a Gradle task):

micronaut default add configuration

micronaut default test maven goal

Once you’ve added the goal/task configuration, click on the Build configuration and click the minus icon to remove it, then click OK. You’re now ready to run/debug your test, which should you give a green build.

Given that this is a per-test configuration change, you’ll either have to repeat it for every test (if you run them individually) or change the default JUnit test configuration. How you want to handle that is completely up to you. If you don’t want to have to do that at all, you can either use Java or Groovy, or go vote on this issue.

In fact, whatever you do, go vote! :)



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    My name is Jason Lee. I am a software developer living in the middle of Oklahoma. I’ve been a professional developer since 1997, using a variety of languages, including Java, Javascript, PHP, Python, Delphi, and even a bit of C#. I currently work for Red Hat on the WildFly/EAP team, where, among other things, I maintain integrations for some MicroProfile specs, OpenTelemetry, Micrometer, Jakarta Faces, and Bean Validation. (Full resume here. LinkedIn profile)

    I am the president of the Oklahoma City JUG, and an occasional speaker at the JUG and a variety of technical conferences.

    On the personal side, I’m active in my church, and enjoy bass guitar, running, fishing, and a variety of martial arts. I’m also married to a beautiful woman, and have two boys, who, thankfully, look like their mother.

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