QEMU is able to emulate many different architecture. Even though it is much slower than accelerated VMs, it's still useful sometimes to have the tests run on a foreign architecture locally, for quicker debug loops.
First ensure you have a suitable VM image (the --timeout is almost necessary when it comes to emulation):
autopkgtest-buildvm-ubuntu-cloud -v --arch arm64 --release jammy --timeout 7200
Then run the tests by specifying the architecture to QEMU. The following command also increases the reboot timeout, because VMs are slower in emulation, and may not be able to reach the login prompt in less than one minute:
autopkgtest gzip -- qemu --qemu-architecture=aarch64 --timeout-reboot 90 autopkgtest-jammy-arm64.img
Foreign arch testing
A particular case of cross-arch testing, is running package for a foreign architecture than the VM's. The typical use-case is testing i386 packages on an amd64 VM. For that, you can specify the -a flag to autopkgtest, and it will automatically setup the required dpkg configuration and install the packages from the right sources (-U mostly here to make sure this example command still runs in the future):
autopkgtest mawk -a i386 -U -- qemu autopkgtest-jammy-amd64.img
Of course, this can be combined with emulated cross-arch, for example to test armhf on emulated arm64:
autopkgtest mawk -a armhf -U -- qemu --qemu-architecture=aarch64 --timeout-reboot 180 autopkgtest-jammy-arm64.img