Heap space issues with JUnit Ant task

When using the JUnit task for Apache Ant I recently came across the following error:

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... [junit] Error occurred during initialization of VM [junit] Could not reserve enough space for object heap [junit] Could not create the Java virtual machine. [junit] java.io.FileNotFoundException: /home/.../junitvmwatcher995964737.properties (No such file or directory) [junit] at java.io.FileInputStream.open(Native Method) [junit] at java.io.FileInputStream.(FileInputStream.java:106) [junit] at java.io.FileReader.(FileReader.java:55) [junit] at org.apache.tools.ant.taskdefs.optional.junit.JUnitTask.executeAsForked(JUnitTask.java:1028) ...

At first I was rather distracted by the FileNotFoundException, but then I recognized that the message "Could not reserve enough space for object heap" might be a pointer to the actual problem.

My build file contained a target for the execution of JUnit tests roughly looking as follows:

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... <target name="junit" depends="jar"> <junit printsummary="true" fork="true" forkmode="perTest" maxmemory="2048m"> <classpath>...</classpath> <batchtest> <fileset dir="${src.dir}" includes="*Test.java"/> </batchtest> </junit> </target> ...

When I decreased the value for the maxmemory attribute the error went away. I thought a rather large value here wouldn't do any harm, as I expected that only the actually required amount of memory would be allocated.

But obviously the JUnit task tries to allocate the total amount of memory up-front, causing the test to fail on my system, which only has 2 GB of RAM altogether.