How do you run JUnit tests in Flatpak Eclipse?

I have Eclipse installed as a Flatpak via Flathub. When I try to run a JUnit 4 suite defined to run all tests within a project, it fails with this exception:

java.lang.IllegalArgumentException: Cannot read testname file.
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.defaultInit(RemoteTestRunner.java:266)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.init(RemoteTestRunner.java:225)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209)

I looked into the source for RemoteTestRunner and found that it is trying to read a file whose path was provided to the runner:

            else if("-testnamefile".equals(args[i].toLowerCase())) { //$NON-NLS-1$
                String testNameFile= args[i+1];
                try {
                    readTestNames(testNameFile);
                } catch (IOException e) {
                    throw new IllegalArgumentException("Cannot read testname file.");        //$NON-NLS-1$
                }
                i++;

            }

Source link

So I examined the command line for the test execution and did find that argument:

-testNameFile /tmp/testNames8297875472451881369.txt

The exception message isn't lying - that file does not exist. The name of the file changes each time it is run, but the file is never created.

I verified from a terminal inside Eclipse and from the Flatpak container via flatpak run --command=sh org.eclipse.Java that I can create, modify, and delete files at /tmp.

This is where I'm stuck. I'm not sure what is supposed to create this temporary file with the test names in it or why it is failing to do so. I see no evidence in Eclipse logs of a failure to write this file. Permissions don't seem to be an issue.

One last observation I did make is that when I open a terminal inside Eclipse and run ls -al /tmp I see all the files from my host machine's /tmp directory. I thought Flatpak specifically blocked /tmp even when file permissions are set to host. However, when I run the sandbox from a terminal (using flatpak run), I see a sandbox version of /tmp that does not match the host. In either case, I can read, write, and modify files in /tmp.

Solution

Turns out this was a bug in the Flatpak permissions and not a configuration issue. This was resolved by the team maintaining the Eclipse Flatpak quickly.

For those that are interested, the Flatpak needed to request read/write access to /tmp.

Here is the issue: https://github.com/flathub/org.eclipse.Java/issues/42

Here is the pull request that fixed it: https://github.com/flathub/org.eclipse.Java/pull/43