# Testing in QEMU

QEMU’s testing infrastructure is fairly complex as it covers everything from unit testing and exercising specific sub-systems all the way to full blown functional tests. To get an overview of the tests you can run `make check-help` from either the source or build tree.

Most (but not all) tests are also integrated as an automated test into the meson build system so can be run directly from the build tree, for example:

    [./pyvenv/bin/]meson test --suite qemu:softfloat

will run just the softfloat tests.

An automated test is written with one of the test frameworks using its generic test functions/classes. The test framework can run the tests and report their success or failure [1].

An automated test has essentially three parts:

1. The test initialization of the parameters, where the expected parameters, like inputs and expected results, are set up;

2. The call to the code that should be tested;

3. An assertion, comparing the result from the previous call with the expected result set during the initialization of the parameters. If the result matches the expected result, the test has been successful; otherwise, it has failed.

The rest of this document will cover the details for specific test groups.

## Testing with “make check”

The “make check” testing family includes most of the C based tests in QEMU.

The usual way to run these tests is:

    make check

which includes QAPI schema tests, unit tests, QTests and some iotests. Different sub-types of “make check” tests will be explained below.

Before running tests, it is best to build QEMU programs first. Some tests expect the executables to exist and will fail with obscure messages if they cannot find them.

### Unit tests

A unit test is responsible for exercising individual software components as a unit, like interfaces, data structures, and functionality, uncovering errors within the boundaries of a component. The verification effort is in the smallest software unit and focuses on the internal processing logic and data structures. A test case of unit tests should be designed to uncover errors due to erroneous computations, incorrect comparisons, or improper control flow [2].

In QEMU, unit tests can be invoked with `make check-unit`. They are simple C tests that typically link to individual QEMU object files and exercise them by calling exported functions.

If you are writing new code in QEMU, consider adding a unit test, especially for utility modules that are relatively stateless or have few dependencies. To add a new unit test:

1. Create a new source file. For example, `tests/unit/foo-test.c`.

2. Write the test. Normally you would include the header file which exports the module API, then verify the interface behaves as expected from your test. The test code should be organized with the glib testing framework. Copying and modifying an existing test is usually a good idea.

3. Add the test to `tests/unit/meson.build`. The unit tests are listed in a dictionary called `tests`. The values are any additional sources and dependencies to be linked with the test. For a simple test whose source is in `tests/unit/foo-test.c`, it is enough to add an entry like:

       {
         ...
         'foo-test': [],
         ...
       }

Since unit tests don’t require environment variables, the simplest way to debug a unit test failure is often directly invoking it or even running it under `gdb`. However there can still be differences in behavior between `make` invocations and your manual run, due to `$MALLOC_PERTURB_` environment variable (which affects memory reclamation and catches invalid pointers better) and gtester options. If necessary, you can run

    make check-unit V=1

and copy the actual command line which executes the unit test, then run it from the command line.

### QTest

QTest is a device emulation testing framework. It can be very useful to test device models; it could also control certain aspects of QEMU (such as virtual clock stepping), with a special purpose “qtest” protocol. Refer to QTest Device Emulation Testing Framework for more details.

QTest cases can be executed with

    make check-qtest

### Writing portable test cases

Both unit tests and qtests can run on POSIX hosts as well as Windows hosts. Care must be taken when writing portable test cases that can be built and run successfully on various hosts. The following list shows some best practices:

- Use portable APIs from glib whenever necessary, e.g.: g_setenv(), g_mkdtemp(), g_mkdir().

- Avoid using hardcoded /tmp for temporary file directory. Use g_get_tmp_dir() instead.

- Bear in mind that Windows has different special string representation for stdin/stdout/stderr and null devices. For example if your test case uses “/dev/fd/2” and “/dev/null” on Linux, remember to use “2” and “nul” on Windows instead. Also IO redirection does not work on Windows, so avoid using “2>nul” whenever necessary.

- If your test cases uses the blkdebug feature, use relative path to pass the config and image file paths in the command line as Windows absolute path contains the delimiter “:” which will confuse the blkdebug parser.

- Use double quotes in your extra QEMU command line in your test cases instead of single quotes, as Windows does not drop single quotes when passing the command line to QEMU.

- Windows opens a file in text mode by default, while a POSIX compliant implementation treats text files and binary files the same. So if your test cases opens a file to write some data and later wants to compare the written data with the original one, be sure to pass the letter ‘b’ as part of the mode string to fopen(), or O_BINARY flag for the open() call.

- If a certain test case can only run on POSIX or Linux hosts, use a proper #ifdef in the codes. If the whole test suite cannot run on Windows, disable the build in the meson.build file.

### QAPI schema tests

The QAPI schema tests validate the QAPI parser used by QMP, by feeding predefined input to the parser and comparing the result with the reference output.

The input/output data is managed under the `tests/qapi-schema` directory. Each test case includes four files that have a common base name:

> - `${casename}.json` - the file contains the JSON input for feeding the parser

> - `${casename}.out` - the file contains the expected stdout from the parser

> - `${casename}.err` - the file contains the expected stderr from the parser

> - `${casename}.exit` - the expected error code

Consider adding a new QAPI schema test when you are making a change on the QAPI parser (either fixing a bug or extending/modifying the syntax). To do this:

1. Add four files for the new case as explained above. For example:

> `$EDITOR tests/qapi-schema/foo.{json,out,err,exit}`.

2. Add the new test in `tests/Makefile.include`. For example:

> `qapi-schema += foo.json`

### check-block

`make check-block` runs a subset of the block layer iotests (the tests that are in the “auto” group). See the “QEMU iotests” section below for more information.

## QEMU iotests

QEMU iotests, under the directory `tests/qemu-iotests`, is the testing framework widely used to test block layer related features. It is higher level than “make check” tests and 99% of the code is written in bash or Python scripts. The testing success criteria is golden output comparison, and the test files are named with numbers.

To run iotests, make sure QEMU is built successfully, then switch to the `tests/qemu-iotests` directory under the build directory, and run `./check` with desired arguments from there.

By default, “raw” format and “file” protocol is used; all tests will be executed, except the unsupported ones. You can override the format and protocol with arguments:

    # test with qcow2 format
    ./check -qcow2
    # or test a different protocol
    ./check -nbd

It’s also possible to list test numbers explicitly:

    # run selected cases with qcow2 format
    ./check -qcow2 001 030 153

Cache mode can be selected with the “-c” option, which may help reveal bugs that are specific to certain cache mode.

More options are supported by the `./check` script, run `./check -h` for help.

### Writing a new test case

Consider writing a tests case when you are making any changes to the block layer. An iotest case is usually the choice for that. There are already many test cases, so it is possible that extending one of them may achieve the goal and save the boilerplate to create one. (Unfortunately, there isn’t a 100% reliable way to find a related one out of hundreds of tests. One approach is using `git grep`.)

Usually an iotest case consists of two files. One is an executable that produces output to stdout and stderr, the other is the expected reference output. They are given the same number in file names. E.g. Test script `055` and reference output `055.out`.

In rare cases, when outputs differ between cache mode `none` and others, a `.out.nocache` file is added. In other cases, when outputs differ between image formats, more than one `.out` files are created ending with the respective format names, e.g. `178.out.qcow2` and `178.out.raw`.

There isn’t a hard rule about how to write a test script, but a new test is usually a (copy and) modification of an existing case. There are a few commonly used ways to create a test:

- A Bash script. It will make use of several environmental variables related to the testing procedure, and could source a group of `common.*` libraries for some common helper routines.

- A Python unittest script. Import `iotests` and create a subclass of `iotests.QMPTestCase`, then call `iotests.main` method. The downside of this approach is that the output is too scarce, and the script is considered harder to debug.

- A simple Python script without using unittest module. This could also import `iotests` for launching QEMU and utilities etc, but it doesn’t inherit from `iotests.QMPTestCase` therefore doesn’t use the Python unittest execution. This is a combination of 1 and 2.

Pick the language per your preference since both Bash and Python have comparable library support for invoking and interacting with QEMU programs. If you opt for Python, it is strongly recommended to write Python 3 compatible code.

Both Python and Bash frameworks in iotests provide helpers to manage test images. They can be used to create and clean up images under the test directory. If no I/O or any protocol specific feature is needed, it is often more convenient to use the pseudo block driver, `null-co://`, as the test image, which doesn’t require image creation or cleaning up. Avoid system-wide devices or files whenever possible, such as `/dev/null` or `/dev/zero`. Otherwise, image locking implications have to be considered. For example, another application on the host may have locked the file, possibly leading to a test failure. If using such devices are explicitly desired, consider adding `locking=off` option to disable image locking.

### Debugging a test case

The following options to the `check` script can be useful when debugging a failing test:

- `-gdb` wraps every QEMU invocation in a `gdbserver`, which waits for a connection from a gdb client. The options given to `gdbserver` (e.g. the address on which to listen for connections) are taken from the `$GDB_OPTIONS` environment variable. By default (if `$GDB_OPTIONS` is empty), it listens on `localhost:12345`. It is possible to connect to it for example with `gdb -iex "target remote $addr"`, where `$addr` is the address `gdbserver` listens on. If the `-gdb` option is not used, `$GDB_OPTIONS` is ignored, regardless of whether it is set or not.

- `-valgrind` attaches a valgrind instance to QEMU. If it detects warnings, it will print and save the log in `$TEST_DIR/<valgrind_pid>.valgrind`. The final command line will be `valgrind --log-file=$TEST_DIR/ <valgrind_pid>.valgrind --error-exitcode=99 $QEMU ...`

- `-d` (debug) just increases the logging verbosity, showing for example the QMP commands and answers.

- `-p` (print) redirects QEMU’s stdout and stderr to the test output, instead of saving it into a log file in `$TEST_DIR/qemu-machine-<random_string>`.

### Test case groups

“Tests may belong to one or more test groups, which are defined in the form of a comment in the test source file. By convention, test groups are listed in the second line of the test file, after the “#!/…” line, like this:

    #!/usr/bin/env python3
    # group: auto quick
    #
    ...

Another way of defining groups is creating the tests/qemu-iotests/group.local file. This should be used only for downstream (this file should never appear in upstream). This file may be used for defining some downstream test groups or for temporarily disabling tests, like this:

    # groups for some company downstream process
    #
    # ci - tests to run on build
    # down - our downstream tests, not for upstream
    #
    # Format of each line is:
    # TEST_NAME TEST_GROUP [TEST_GROUP ]...

    013 ci
    210 disabled
    215 disabled
    our-ugly-workaround-test down ci

Note that the following group names have a special meaning:

- quick: Tests in this group should finish within a few seconds.

- auto: Tests in this group are used during “make check” and should be runnable in any case. That means they should run with every QEMU binary (also non-x86), with every QEMU configuration (i.e. must not fail if an optional feature is not compiled in - but reporting a “skip” is ok), work at least with the qcow2 file format, work with all kind of host filesystems and users (e.g. “nobody” or “root”) and must not take too much memory and disk space (since CI pipelines tend to fail otherwise).

- disabled: Tests in this group are disabled and ignored by check.

## Container based tests

### Introduction

The container testing framework in QEMU utilizes public images to build and test QEMU in predefined and widely accessible Linux environments. This makes it possible to expand the test coverage across distros, toolchain flavors and library versions. The support was originally written for Docker although we also support Podman as an alternative container runtime. Although many of the target names and scripts are prefixed with “docker” the system will automatically run on whichever is configured.

The container images are also used to augment the generation of tests for testing TCG. See Testing with “make check-tcg” for more details.

### Docker Prerequisites

Install “docker” with the system package manager and start the Docker service on your development machine, then make sure you have the privilege to run Docker commands. Typically it means setting up passwordless `sudo docker` command or login as root. For example:

    $ sudo yum install docker
    $ # or `apt-get install docker` for Ubuntu, etc.
    $ sudo systemctl start docker
    $ sudo docker ps

The last command should print an empty table, to verify the system is ready.

An alternative method to set up permissions is by adding the current user to “docker” group and making the docker daemon socket file (by default `/var/run/docker.sock`) accessible to the group:

    $ sudo groupadd docker
    $ sudo usermod $USER -a -G docker
    $ sudo chown :docker /var/run/docker.sock

Note that any one of above configurations makes it possible for the user to exploit the whole host with Docker bind mounting or other privileged operations. So only do it on development machines.

### Podman Prerequisites

Install “podman” with the system package manager.

    $ sudo dnf install podman
    $ podman ps

The last command should print an empty table, to verify the system is ready.

### Quickstart

From source tree, type `make docker-help` to see the help. Testing can be started without configuring or building QEMU (`configure` and `make` are done in the container, with parameters defined by the make target):

    make docker-test-build@debian

This will create a container instance using the `debian` image (the image is downloaded and initialized automatically), in which the `test-build` job is executed.

### Registry

The QEMU project has a container registry hosted by GitLab at `registry.gitlab.com/qemu-project/qemu` which will automatically be used to pull in pre-built layers. This avoids unnecessary strain on the distro archives created by multiple developers running the same container build steps over and over again. This can be overridden locally by using the `NOCACHE` build option:

    make docker-image-debian-arm64-cross NOCACHE=1

### Images

Along with many other images, the `debian` image is defined in a Dockerfile in `tests/docker/dockerfiles/`, called `debian.docker`. `make docker-help` command will list all the available images.

A `.pre` script can be added beside the `.docker` file, which will be executed before building the image under the build context directory. This is mainly used to do necessary host side setup. One such setup is `binfmt_misc`, for example, to make qemu-user powered cross build containers work.

Most of the existing Dockerfiles were written by hand, simply by creating a a new `.docker` file under the `tests/docker/dockerfiles/` directory. This has led to an inconsistent set of packages being present across the different containers.

Thus going forward, QEMU is aiming to automatically generate the Dockerfiles using the `lcitool` program provided by the `libvirt-ci` project:

> https://gitlab.com/libvirt/libvirt-ci

`libvirt-ci` contains an `lcitool` program as well as a list of mappings to distribution package names for a wide variety of third party projects. `lcitool` applies the mappings to a list of build pre-requisites in `tests/lcitool/projects/qemu.yml`, determines the list of native packages to install on each distribution, and uses them to generate build environments (dockerfiles and Cirrus CI variable files) that are consistent across OS distribution.

#### Adding new build pre-requisites

When preparing a patch series that adds a new build pre-requisite to QEMU, the prerequisites should to be added to `tests/lcitool/projects/qemu.yml` in order to make the dependency available in the CI build environments.

In the simple case where the pre-requisite is already known to `libvirt-ci` the following steps are needed:

> - Edit `tests/lcitool/projects/qemu.yml` and add the pre-requisite

> - Run `make lcitool-refresh` to re-generate all relevant build environment manifests

It may be that `libvirt-ci` does not know about the new pre-requisite. If that is the case, some extra preparation steps will be required first to contribute the mapping to the `libvirt-ci` project:

> - Fork the `libvirt-ci` project on gitlab

> - Add an entry for the new build prerequisite to `lcitool/facts/mappings.yml`, listing its native package name on as many OS distros as practical. Run `python -m pytest --regenerate-output` and check that the changes are correct.

> - Commit the `mappings.yml` change together with the regenerated test files, and submit a merge request to the `libvirt-ci` project. Please note in the description that this is a new build pre-requisite desired for use with QEMU.

> - CI pipeline will run to validate that the changes to `mappings.yml` are correct, by attempting to install the newly listed package on all OS distributions supported by `libvirt-ci`.

> - Once the merge request is accepted, go back to QEMU and update the `tests/lcitool/libvirt-ci` submodule to point to a commit that contains the `mappings.yml` update. Then add the prerequisite and run `make lcitool-refresh`.

> - Please also trigger gitlab container generation pipelines on your change for as many OS distros as practical to make sure that there are no obvious breakages when adding the new pre-requisite. Please see CI documentation page on how to trigger gitlab CI pipelines on your change.

For enterprise distros that default to old, end-of-life versions of the Python runtime, QEMU uses a separate set of mappings that work with more recent versions. These can be found in `tests/lcitool/mappings.yml`. Modifying this file should not be necessary unless the new pre-requisite is a Python library or tool.

#### Adding new OS distros

In some cases `libvirt-ci` will not know about the OS distro that is desired to be tested. Before adding a new OS distro, discuss the proposed addition:

> - Send a mail to qemu-devel, copying people listed in the MAINTAINERS file for `Build and test automation`.

>   There are limited CI compute resources available to QEMU, so the cost/benefit tradeoff of adding new OS distros needs to be considered.

> - File an issue at https://gitlab.com/libvirt/libvirt-ci/-/issues pointing to the qemu-devel mail thread in the archives.

>   This alerts other people who might be interested in the work to avoid duplication, as well as to get feedback from libvirt-ci maintainers on any tips to ease the addition

Assuming there is agreement to add a new OS distro then

> - Fork the `libvirt-ci` project on gitlab

> - Add metadata under `lcitool/facts/targets/` for the new OS distro. There might be code changes required if the OS distro uses a package format not currently known. The `libvirt-ci` maintainers can advise on this when the issue is filed.

> - Edit the `lcitool/facts/mappings.yml` change to add entries for the new OS, listing the native package names for as many packages as practical. Run `python -m pytest --regenerate-output` and check that the changes are correct.

> - Commit the changes to `lcitool/facts` and the regenerated test files, and submit a merge request to the `libvirt-ci` project. Please note in the description that this is a new build pre-requisite desired for use with QEMU

> - CI pipeline will run to validate that the changes to `mappings.yml` are correct, by attempting to install the newly listed package on all OS distributions supported by `libvirt-ci`.

> - Once the merge request is accepted, go back to QEMU and update the `libvirt-ci` submodule to point to a commit that contains the `mappings.yml` update.

### Tests

Different tests are added to cover various configurations to build and test QEMU. Docker tests are the executables under `tests/docker` named `test-*`. They are typically shell scripts and are built on top of a shell library, `tests/docker/common.rc`, which provides helpers to find the QEMU source and build it.

The full list of tests is printed in the `make docker-help` help.

### Debugging a Docker test failure

When CI tasks, maintainers or yourself report a Docker test failure, follow the below steps to debug it:

1. Locally reproduce the failure with the reported command line. E.g. run `make docker-test-mingw@fedora-win64-cross J=8`.

2. Add “V=1” to the command line, try again, to see the verbose output.

3. Further add “DEBUG=1” to the command line. This will pause in a shell prompt in the container right before testing starts. You could either manually build QEMU and run tests from there, or press `Ctrl`+`d` to let the Docker testing continue.

4. If you press `Ctrl`+`d`, the same building and testing procedure will begin, and will hopefully run into the error again. After that, you will be dropped to the prompt for debug.

### Options

Various options can be used to affect how Docker tests are done. The full list is in the `make docker` help text. The frequently used ones are:

- `V=1`: the same as in top level `make`. It will be propagated to the container and enable verbose output.

- `J=$N`: the number of parallel tasks in make commands in the container, similar to the `-j $N` option in top level `make`. (The `-j` option in top level `make` will not be propagated into the container.)

- `DEBUG=1`: enables debug. See the previous “Debugging a Docker test failure” section.

## Thread Sanitizer

Thread Sanitizer (TSan) is a tool which can detect data races. QEMU supports building and testing with this tool.

For more information on TSan:

https://github.com/google/sanitizers/wiki/ThreadSanitizerCppManual

### Thread Sanitizer in Docker

TSan is currently supported in the ubuntu2204 docker.

The test-tsan test will build using TSan and then run make check.

    make docker-test-tsan@ubuntu2204

TSan warnings under docker are placed in files located at build/tsan/.

We recommend using DEBUG=1 to allow launching the test from inside the docker, and to allow review of the warnings generated by TSan.

### Building and Testing with TSan

It is possible to build and test with TSan, with a few additional steps. These steps are normally done automatically in the docker.

TSan is supported for clang and gcc. One particularity of sanitizers is that all the code, including shared objects dependencies, should be built with it. In the case of TSan, any synchronization primitive from glib (GMutex for instance) will not be recognized, and will lead to false positives.

To build a tsan version of glib:

    $ git clone --depth=1 --branch=2.81.0 https://github.com/GNOME/glib.git
    $ cd glib
    $ CFLAGS="-O2 -g -fsanitize=thread" meson build
    $ ninja -C build

To configure the build for TSan:

    ../configure --enable-tsan \
                 --disable-werror --extra-cflags="-O0"

When executing qemu, don’t forget to point to tsan glib:

    $ glib_dir=/path/to/glib
    $ export LD_LIBRARY_PATH=$glib_dir/build/gio:$glib_dir/build/glib:$glib_dir/build/gmodule:$glib_dir/build/gobject:$glib_dir/build/gthread
    # check correct version is used
    $ ldd build/qemu-x86_64 | grep glib
    $ qemu-system-x86_64 ...

The runtime behavior of TSAN is controlled by the TSAN_OPTIONS environment variable.

More information on the TSAN_OPTIONS can be found here:

https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags

For example:

    export TSAN_OPTIONS=suppressions=<path to qemu>/tests/tsan/suppressions.tsan \
                        detect_deadlocks=false history_size=7 exitcode=0 \
                        log_path=<build path>/tsan/tsan_warning

The above exitcode=0 has TSan continue without error if any warnings are found. This allows for running the test and then checking the warnings afterwards. If you want TSan to stop and exit with error on warnings, use exitcode=66.

### TSan Suppressions

Keep in mind that for any data race warning, although there might be a data race detected by TSan, there might be no actual bug here. TSan provides several different mechanisms for suppressing warnings. In general it is recommended to fix the code if possible to eliminate the data race rather than suppress the warning.

A few important files for suppressing warnings are:

tests/tsan/suppressions.tsan - Has TSan warnings we wish to suppress at runtime. The comment on each suppression will typically indicate why we are suppressing it. More information on the file format can be found here:

https://github.com/google/sanitizers/wiki/ThreadSanitizerSuppressions

tests/tsan/ignore.tsan - Has TSan warnings we wish to disable at compile time for test or debug. Add flags to configure to enable:

“–extra-cflags=-fsanitize-blacklist=<src path>/tests/tsan/ignore.tsan”

More information on the file format can be found here under “Blacklist Format”:

https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags

### TSan Annotations

include/qemu/tsan.h defines annotations. See this file for more descriptions of the annotations themselves. Annotations can be used to suppress TSan warnings or give TSan more information so that it can detect proper relationships between accesses of data.

Annotation examples can be found here:

https://github.com/llvm/llvm-project/tree/master/compiler-rt/test/tsan/

Good files to start with are: annotate_happens_before.cpp and ignore_race.cpp

The full set of annotations can be found here:

https://github.com/llvm/llvm-project/blob/master/compiler-rt/lib/tsan/rtl/tsan_interface_ann.cpp

## docker-binfmt-image-debian-% targets

It is possible to combine Debian’s bootstrap scripts with a configured `binfmt_misc` to bootstrap a number of Debian’s distros including experimental ports not yet supported by a released OS. This can simplify setting up a rootfs by using docker to contain the foreign rootfs rather than manually invoking chroot.

### Setting up `binfmt_misc`

You can use the script `qemu-binfmt-conf.sh` to configure a QEMU user binary to automatically run binaries for the foreign architecture. While the scripts will try their best to work with dynamically linked QEMU’s a statically linked one will present less potential complications when copying into the docker image. Modern kernels support the `F` (fix binary) flag which will open the QEMU executable on setup and avoids the need to find and re-open in the chroot environment. This is triggered with the `--persistent` flag.

### Example invocation

For example to setup the HPPA ports builds of Debian:

    make docker-binfmt-image-debian-sid-hppa \
      DEB_TYPE=sid DEB_ARCH=hppa \
      DEB_URL=http://ftp.ports.debian.org/debian-ports/ \
      DEB_KEYRING=/usr/share/keyrings/debian-ports-archive-keyring.gpg \
      EXECUTABLE=(pwd)/qemu-hppa V=1

The `DEB_` variables are substitutions used by `debian-bootstrap.pre` which is called to do the initial debootstrap of the rootfs before it is copied into the container. The second stage is run as part of the build. The final image will be tagged as `qemu/debian-sid-hppa`.

## VM testing

This test suite contains scripts that bootstrap various guest images that have necessary packages to build QEMU. The basic usage is documented in `Makefile` help which is displayed with `make vm-help`.

### Quickstart

Run `make vm-help` to list available make targets. Invoke a specific make command to run build test in an image. For example, `make vm-build-freebsd` will build the source tree in the FreeBSD image. The command can be executed from either the source tree or the build dir; if the former, `./configure` is not needed. The command will then generate the test image in `./tests/vm/` under the working directory.

Note: images created by the scripts accept a well-known RSA key pair for SSH access, so they SHOULD NOT be exposed to external interfaces if you are concerned about attackers taking control of the guest and potentially exploiting a QEMU security bug to compromise the host.

### QEMU binaries

By default, `qemu-system-x86_64` is searched in $PATH to run the guest. If there isn’t one, or if it is older than 2.10, the test won’t work. In this case, provide the QEMU binary in env var: `QEMU=/path/to/qemu-2.10+`.

Likewise the path to `qemu-img` can be set in QEMU_IMG environment variable.

### Make jobs

The `-j$X` option in the make command line is not propagated into the VM, specify `J=$X` to control the make jobs in the guest.

### Debugging

Add `DEBUG=1` and/or `V=1` to the make command to allow interactive debugging and verbose output. If this is not enough, see the next section. `V=1` will be propagated down into the make jobs in the guest.

### Manual invocation

Each guest script is an executable script with the same command line options. For example to work with the netbsd guest, use `$QEMU_SRC/tests/vm/netbsd`:

    $ cd $QEMU_SRC/tests/vm

    # To bootstrap the image
    $ ./netbsd --build-image --image /var/tmp/netbsd.img
    <...>

    # To run an arbitrary command in guest (the output will not be echoed unless
    # --debug is added)
    $ ./netbsd --debug --image /var/tmp/netbsd.img uname -a

    # To build QEMU in guest
    $ ./netbsd --debug --image /var/tmp/netbsd.img --build-qemu $QEMU_SRC

    # To get to an interactive shell
    $ ./netbsd --interactive --image /var/tmp/netbsd.img sh

### Adding new guests

Please look at existing guest scripts for how to add new guests.

Most importantly, create a subclass of BaseVM and implement `build_image()` method and define `BUILD_SCRIPT`, then finally call `basevm.main()` from the script’s `main()`.

- Usually in `build_image()`, a template image is downloaded from a predefined URL. `BaseVM._download_with_cache()` takes care of the cache and the checksum, so consider using it.

- Once the image is downloaded, users, SSH server and QEMU build deps should be set up:

  - Root password set to `BaseVM.ROOT_PASS`

  - User `BaseVM.GUEST_USER` is created, and password set to `BaseVM.GUEST_PASS`

  - SSH service is enabled and started on boot, `$QEMU_SRC/tests/keys/id_rsa.pub` is added to ssh’s `authorized_keys` file of both root and the normal user

  - DHCP client service is enabled and started on boot, so that it can automatically configure the virtio-net-pci NIC and communicate with QEMU user net (10.0.2.2)

  - Necessary packages are installed to untar the source tarball and build QEMU

- Write a proper `BUILD_SCRIPT` template, which should be a shell script that untars a raw virtio-blk block device, which is the tarball data blob of the QEMU source tree, then configure/build it. Running “make check” is also recommended.

## Image fuzzer testing

An image fuzzer was added to exercise format drivers. Currently only qcow2 is supported. To start the fuzzer, run

    tests/image-fuzzer/runner.py -c '[["qemu-img", "info", "$test_img"]]' /tmp/test qcow2

Alternatively, some command different from `qemu-img info` can be tested, by changing the `-c` option.

## Functional tests using Python

A functional test focuses on the functional requirement of the software, attempting to find errors like incorrect functions, interface errors, behavior errors, and initialization and termination errors [3].

The `tests/functional` directory hosts functional tests written in Python. You can run the functional tests simply by executing:

    make check-functional

See Functional testing with Python for more details.

## Testing with “make check-tcg”

The check-tcg tests are intended for simple smoke tests of both linux-user and softmmu TCG functionality. However to build test programs for guest targets you need to have cross compilers available. If your distribution supports cross compilers you can do something as simple as:

    apt install gcc-aarch64-linux-gnu

The configure script will automatically pick up their presence. Sometimes compilers have slightly odd names so the availability of them can be prompted by passing in the appropriate configure option for the architecture in question, for example:

    $(configure) --cross-cc-aarch64=aarch64-cc

There is also a `--cross-cc-cflags-ARCH` flag in case additional compiler flags are needed to build for a given target.

If you have the ability to run containers as the user the build system will automatically use them where no system compiler is available. For architectures where we also support building QEMU we will generally use the same container to build tests. However there are a number of additional containers defined that have a minimal cross-build environment that is only suitable for building test cases. Sometimes we may use a bleeding edge distribution for compiler features needed for test cases that aren’t yet in the LTS distros we support for QEMU itself.

See Container based tests for more details.

### Running subset of tests

You can build the tests for one architecture:

    make build-tcg-tests-$TARGET

And run with:

    make run-tcg-tests-$TARGET

Adding `V=1` to the invocation will show the details of how to invoke QEMU for the test which is useful for debugging tests.

### Running individual tests

Tests can also be run directly from the test build directory. If you run `make help` from the test build directory you will get a list of all the tests that can be run. Please note that same binaries are used in multiple tests, for example:

    make run-plugin-test-mmap-with-libinline.so

will run the mmap test with the `libinline.so` TCG plugin. The gdbstub tests also re-use the test binaries but while exercising gdb.

### TCG test dependencies

The TCG tests are deliberately very light on dependencies and are either totally bare with minimal gcc lib support (for system-mode tests) or just glibc (for linux-user tests). This is because getting a cross compiler to work with additional libraries can be challenging.

## Other TCG Tests

There are a number of out-of-tree test suites that are used for more extensive testing of processor features.

### KVM Unit Tests

The KVM unit tests are designed to run as a Guest OS under KVM but there is no reason why they can’t exercise the TCG as well. It provides a minimal OS kernel with hooks for enabling the MMU as well as reporting test results via a special device:

    https://git.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git

### Linux Test Project

The LTP is focused on exercising the syscall interface of a Linux kernel. It checks that syscalls behave as documented and strives to exercise as many corner cases as possible. It is a useful test suite to run to exercise QEMU’s linux-user code:

    https://linux-test-project.github.io/

## GCC gcov support

`gcov` is a GCC tool to analyze the testing coverage by instrumenting the tested code. To use it, configure QEMU with `--enable-gcov` option and build. Then run the tests as usual.

If you want to gather coverage information on a single test the `make clean-gcda` target can be used to delete any existing coverage information before running a single test.

You can generate a HTML coverage report by executing `make coverage-html` which will create `meson-logs/coveragereport/index.html`.

Further analysis can be conducted by running the `gcov` command directly on the various .gcda output files. Please read the `gcov` documentation for more information.

## Flaky tests

A flaky test is defined as a test that exhibits both a passing and a failing result with the same code on different runs. Some usual reasons for an intermittent/flaky test are async wait, concurrency, and test order dependency [4].

In QEMU, tests that are identified to be flaky are normally disabled by default. Set the QEMU_TEST_FLAKY_TESTS environment variable before running the tests to enable them.

## References

[1]

Sommerville, Ian (2016). Software Engineering. p. 233.

[2]

Pressman, Roger S. & Maxim, Bruce R. (2020). Software Engineering, A Practitioner’s Approach. p. 48, 376, 378, 381.

[3]

Pressman, Roger S. & Maxim, Bruce R. (2020). Software Engineering, A Practitioner’s Approach. p. 388.

[4]

Luo, Qingzhou, et al. An empirical analysis of flaky tests. Proceedings of the 22nd ACM SIGSOFT International Symposium on Foundations of Software Engineering. 2014.