StringInputStream.java should be in main source folder

In the change report of the new commons-io 2.12.0, I read:

"Add StringInputStream"
as a new feature.

Now I went looking for it in the 2.12.0 javadoc and binary, and didn't find it.

However, I did find that source file in the "test" sources, instead of the normal sources.

https://github.com/apache/commons-io/blob/master/src/test/java/org/apache/commons/io/input/StringInputStream.java

Is this intentional? If this is, then the change report is rather confusing. If it's not intentional, then maybe this source was committed in the wrong location or had to move to the normal sources?