So you think you can skip tests? The "dark side" of Maven

maven May 31, 2016

Tests are the light side of programming. Period. Running test cases is one of the fundamental duty of every build automation system - including Maven. Even if it's a kind of ritual and the determinant of style, every experienced programmer knows that sometimes things just have to be MacGavyered instantly. But how to fold up a late night app version using only Maven, bottle of ketchup and an old shoelace if our tests just don't pass?

#1 I'll fix that later (-DskipTests)

This one is quite straightforward - running: mvn clean install -DskipTests skips tests execution:

[INFO] --- maven-compiler-plugin:3.5.1:testCompile (default-testCompile) @ skip-test-playground ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to /home/user/workspace/skip-test-playground/target/test-classes
[INFO] 
[INFO] --- maven-surefire-plugin:2.10:test (default-test) @ skip-test-playground ---
[INFO] Tests are skipped.
[INFO] 
[INFO] --- maven-jar-plugin:2.2:jar (default-jar) @ skip-test-playground ---
[INFO] Building jar: /home/user/workspace/skip-test-playground/target/skip-test-playground-1.0-SNAPSHOT.jar

Problem solved? Now it's time for a quick release...

#2 Just release it, please...

When using Maven Release Plugin constructs like mvn release:perform -DskipTests don't work at all. To understand why, let's look at the docs first:

release:perform will fork a new Maven instance to build the checked-out project. This new Maven instance will use the same system configuration and Maven profiles used by the one running the release:perform goal.

The problem is that -DskipTests is neither a system configuration nor a profile - it's a command line property. Release plugin creates a forked process for each of our projects and the property won't be propagated automatically.

The solution is to use -Darguments="-DskipTests". This property defines additional arguments that will be passed to each forked Maven process. So this mean "skip tests for every project you are trying to release".

#3 No time to explain - don't even compile!

The last one is probably the most reckless one. In each of the cases before we don't want to run the tests, but they will be compiled anyway:

[INFO] Compiling 1 source file to /home/user/workspace/skip-test-playground/target/test-classes

But what if our tests don't even compile? In 99.9999% of cases this should be a sufficent warning - something gone seriously wrong. If you are a fan of the remaining 0.0001% or you have nothing left to loose you can use the mysterious property called maven.test.skip. How does it work? Running mvn clean install -Dmaven.test.skip=true just won't compile test sources.

[INFO] --- maven-compiler-plugin:3.5.1:testCompile (default-testCompile) @ skip-test-playground ---
[INFO] Not compiling test sources
[INFO] 
[INFO] --- maven-surefire-plugin:2.10:test (default-test) @ skip-test-playground ---
[INFO] Tests are skipped.
[INFO] 
[INFO] --- maven-jar-plugin:2.2:jar (default-jar) @ skip-test-playground ---
[INFO] Building jar: /home/user/workspace/skip-test-playground/target/skip-test-playground-1.0-SNAPSHOT.jar
Conclusions

There are many real-life scenarios for skipping the tests and not all of them are a pure evil :-) However, consider taking a day off before even thinking of maven.test.skip=true and remember:
This should be a meme

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Mike Kowalski

Full-stack developer (JVM mostly) believing in Software Craftsmanship, Scrum, and the power of fresh espresso