When the surfire plugin execute the test in a forked environment, it starts a new cmd process. For this environment the registry hack will set the working directory to "c:\dev" and the JVM is started from within.
parent.exists()
Resolves the path against the directory from which the JVM was started. Which means the test checks the presence of file "C:/dev/some-dir/target/generated-resources/stuff.xml".
parent.getAbsoluteFile().exists()
This checks the presence of the file with it's absolute name, the one you expected to check.
see also the EVALUATION comment for this filed JDK bug
4483097 : File returned by getAbsoluteFile() may not refer to the original file