How IntelliJ IDEA played a dirty trick on me

I am going to talk briefly about something that happened to me the other day while writing some unit tests. I discovered a feature from IntelliJ IDEA that was hidden to me and bugged me for a few minutes.

Writing my test

While doing Test Driven Development (TDD), I wrote a test for a method where passing a null value, it would throw an exception. In our project we use AssertJ, a good library for assertions which I personally love compared to Hamcrest.

The assertion of the test looked like this:

assertThatThrownBy(() ->
    sut.doSomeWork(null)
).isInstanceOf(NullPointerException.class);

I wanted the code to throw a NullPointerException when a null value was passed, so I called Objects.requireNonNull(...). Additionally, I thought of adding a @NotNull annotation to improve its usability (specially if we later decide to use Kotlin 😁).

The method looked like this:

import org.jetbrains.annotations.NotNull;

public String doSomeWork(@NotNull final String str) {
    Objects.requireNonNull(str, "Parameter 'str' must not be null");

    // ...
}

I run my test suite and the test failed with the following error:

Expecting actual throwable to be an instance of:
  java.lang.NullPointerException
but was:
  java.lang.IllegalArgumentException: Parameter 'str' must not be null
	at java.util.Objects.requireNonNull(Objects.java:228)
    ...

So I thought:

My bad, I made a mistake. Let us replace the expected exception and problem solved.

Indeed that solved my problem.

Getting confused

When I finished writing my code, I commited my changes and pushed them to my remote GIT repository.

What was my surprise when my Continuous Integration (CI) pipeline failed with the next message:

Expecting actual throwable to be an instance of:
  java.lang.IllegalArgumentException
but was:
  java.lang.NullPointerException: Parameter 'str' must not be null
	at java.util.Objects.requireNonNull(Objects.java:228)
    ...

This was me puzzled. What is going on!?

Following, I did something I admit I should have done in the beginning, I went to check the implementation of Objects.requireNonNull(...).

It looks like this in Java 8:

public static <T> T requireNonNull(T var0, String var1) {
    if (var0 == null) {
        throw new NullPointerException(var1);
    } else {
        return var0;
    }
}

So I actually wrote the test right in the first place! Why is then IntelliJ IDEA failing with a different error?

Finding out the issue

I did some research and it turns out this is not a bug, it is a feature from IntelliJ IDEA 🤦‍♂️. Apparently IntelliJ IDEA adds some runtime assertions for @NotNull annotated methods and parameters.

Fortunately, this can be disabled in the Settings (or Preferences, depending on your OS) of IntelliJ IDEA. Go to Build, Execution, Deployment > Compiler. We must disable the option Add runtime assertions for notnull-annotated methods and parameters:

This is the option to disable.

After disabling that option, my test had the same result both in my machine and in the CI pipeline. Nice!

Note: If that did not work straight away, you may need to invalidate cache and restart your IDE and/or rebuild your project.

If you were puzzled like me and were looking for a solution or just to throw some light into the issue, I hope this was helpful!

Thanks for reading!