Can't use local deb binaries on a readonly testbed

[Leo Arias]

In the ubuntu-ota-tests project, the debian/control defines a python package python3-ubuntu-ota-tests. We need this package to be in the PYTHONPATH for it to be found by the upgrade hook.

If we run
$ adt-run --unbuilt-tree . --- ssh -s adb

We will get:
dpkg-buildpackage: error: fakeroot not found, either install the fakeroot
package, specify a command with the -r option, or run this as root
blame: .
badpkg: rules build failed with exit code 2
adt-run [09:57:07]: ERROR: erroneous package: rules build failed with exit code 2
Exit request sent.

If we run:
$ bzr bd --result-dir=/tmp -- -uc -us
$ adt-run --binary /tmp/python3-ubuntu-ota-tests*.deb --built-tree . --- ssh -s ./adb-reboot-to-recovery

We will get:
sh: 1: cannot create /etc/apt/preferences.d/90autopkgtest: Read-only file system
Exit request sent.
<VirtSubproc>: failure: copydown destination failed, status 2
adt-run [09:49:48]: ERROR: testbed failed: cannot send to testbed: ['BrokenPipeError: [Errno 32] Broken pipe\n']

I think the right solution for this case is the second one, using a built-tree, and send the deb to the testbed. So what we are missing is to install those debs in the tmp directory just as the rest of dependencies.

[Leo Arias (elopio)]

We can use some workarounds, like hack the PYTHONPATH, or cd into the directory that has the python package, so it will be found in the cwd. We might need both things for some tests.
What will make the tests easier is just to have it installed.

[Barry Warsaw (barry)]

Of course, when we reuse python3-ubuntu-ota-tests in other packages, it will have to be installed. I think we'd like this package's own tests to run the same way (i.e. not fiddle with sys.path or cd).

[Leo Arias (elopio)]

Another possible workaround is to make the device writable, install fakeroot, and then make it read-only again. This is not ideal of course, as we want to keep the device read-only. I'm just mentioning it, but don't try it at home.

[Leo Arias (elopio)]

Making the device writable and installing all the packages required for the build is not an option either. In the end we get the same error as when we build the package on the host:

sh: 1: cannot create /etc/apt/preferences.d/90autopkgtest: Read-only file system