The Rust project runs a wide variety of different tests, orchestrated by
the build system (
x.py test). The main test harness for testing the
compiler itself is a tool called compiletest (located in the
src/tools/compiletest directory). This section gives a brief
overview of how the testing framework is setup, and then gets into some
of the details on how to run tests as well as how to
add new tests.
The compiletest tests are located in the tree in the
directory. Immediately within you will see a series of subdirectories
run-make, and so forth). Each of those directories is
called a test suite – they house a group of tests that are run in
a distinct mode.
Here is a brief summary of the test suites and what they mean. In some cases, the test suites are linked to parts of the manual that give more details.
ui– tests that check the exact stdout/stderr from compilation and/or running the test
run-pass-valgrind– tests that ought to run with valgrind
run-fail– tests that are expected to compile but then panic during execution
compile-fail– tests that are expected to fail compilation.
parse-fail– tests that are expected to fail to parse
pretty– tests targeting the Rust "pretty printer", which generates valid Rust code from the AST
debuginfo– tests that run in gdb or lldb and query the debug info
codegen– tests that compile and then test the generated LLVM code to make sure that the optimizations we want are taking effect. See LLVM docs for how to write such tests.
assembly– similar to
codegentests, but verifies assembly output to make sure LLVM target backend can handle provided code.
mir-opt– tests that check parts of the generated MIR to make sure we are building things correctly or doing the optimizations we expect.
incremental– tests for incremental compilation, checking that when certain modifications are performed, we are able to reuse the results from previous compilations.
run-make– tests that basically just execute a
Makefile; the ultimate in flexibility but quite annoying to write.
rustdoc– tests for rustdoc, making sure that the generated files contain the expected documentation.
*-fulldeps– same as above, but indicates that the test depends on things other than
libstd(and hence those things must be built)
The Rust build system handles running tests for various other things, including:
Tidy – This is a custom tool used for validating source code style and formatting conventions, such as rejecting long lines. There is more information in the section on coding conventions.
./x.py test tidy
Formatting – Rustfmt is integrated with the build system to enforce uniform style across the compiler. In the CI, we check that the formatting is correct. The formatting check is also automatically run by the Tidy tool mentioned above.
./x.py fmt --checkchecks formatting an exits with an error if formatting is needed.
./x.py fmtruns rustfmt on the codebase.
./x.py test tidy --blessdoes formatting before doing other tidy checks.
Unit tests – The Rust standard library and many of the Rust packages include typical Rust
#[test]unittests. Under the hood,
cargo teston each package to run all the tests.
./x.py test src/libstd
Doc tests – Example code embedded within Rust documentation is executed via
rustdoc --test. Examples:
./x.py test src/doc– Runs
rustdoc --testfor all documentation in
./x.py test --doc src/libstd– Runs
rustdoc --teston the standard library.
Link checker – A small tool for verifying
hreflinks within documentation.
./x.py test src/tools/linkchecker
Dist check – This verifies that the source distribution tarball created by the build system will unpack, build, and run all tests.
./x.py test distcheck
Tool tests – Packages that are included with Rust have all of their tests run as well (typically by running
cargo testwithin their directory). This includes things such as cargo, clippy, rustfmt, rls, miri, bootstrap (testing the Rust build system itself), etc.
Cargo test – This is a small tool which runs
cargo teston a few significant projects (such as
tokei, etc.) just to ensure there aren't any significant regressions.
./x.py test src/tools/cargotest
When a Pull Request is opened on Github, Azure Pipelines will automatically
launch a build that will run all tests on some configurations
(x86_64-gnu-llvm-6.0 linux. x86_64-gnu-tools linux, mingw-check linux). In
essence, it runs
./x.py test after building for each of them.
The integration bot bors is used for coordinating merges to the master branch. When a PR is approved, it goes into a queue where merges are tested one at a time on a wide set of platforms using Azure Pipelines (currently over 50 different configurations). Most platforms only run the build steps, some run a restricted set of tests, only a subset run the full suite of tests (see Rust's platform tiers).
The Rust tree includes Docker image definitions for the platforms used on
Azure Pipelines in
src/ci/docker. The script
src/ci/docker/run.sh is used to build
the Docker image, run it, build Rust within the image, and run the tests.
You can run these images on your local development machine. This can be
helpful to test environments different from your local system. First you will
need to install Docker on a Linux, Windows, or macOS system (typically Linux
will be much faster than Windows or macOS because the later use virtual
machines to emulate a Linux environment). To enter interactive mode which will
start a bash shell in the container, run
src/ci/docker/run.sh --dev <IMAGE>
<IMAGE> is one of the directory names in
src/ci/docker (for example
x86_64-gnu is a fairly standard Ubuntu environment).
The docker script will mount your local rust source tree in read-only mode,
obj directory in read-write mode. All of the compiler artifacts will
be stored in the
obj directory. The shell will start out in the
directory. From there, you can run
../src/ci/run.sh which will run the build
as defined by the image.
Alternatively, you can run individual commands to do specific tasks. For
example, you can run
python3 ../x.py test src/test/ui to just run UI tests.
Note that there is some configuration in the
src/ci/run.sh script that you
may need to recreate. Particularly, set
submodules = false in your
config.toml so that it doesn't attempt to modify the read-only directory.
Some additional notes about using the Docker images:
- Some of the std tests require IPv6 support. Docker on Linux seems to have it
disabled by default. Run the commands in
enable-docker-ipv6.shto enable IPv6 before creating the container. This only needs to be done once.
- The container will be deleted automatically when you exit the shell, however
the build artifacts persist in the
objdirectory. If you are switching between different Docker images, the artifacts from previous environments stored in the
objdirectory may confuse the build system. Sometimes you will need to delete parts or all of the
objdirectory before building inside the container.
- The container is bare-bones, with only a minimal set of packages. You may
want to install some things like
apt install less vim.
- You can open multiple shells in the container. First you need the container
name (a short hash), which is displayed in the shell prompt, or you can run
docker container lsoutside of the container to list the available containers. With the container name, run
docker exec -it <CONTAINER> /bin/bashwhere
<CONTAINER>is the container name like
Tests may be run on a remote machine (e.g. to test builds for a different
architecture). This is done using
remote-test-client on the build machine
to send test programs to
remote-test-server running on the remote machine.
remote-test-server executes the test programs and sends the results back to
the build machine.
remote-test-server provides unauthenticated remote code
execution so be careful where it is used.
To do this, first build
remote-test-server for the remote
machine, e.g. for RISC-V
./x.py build src/tools/remote-test-server --target riscv64gc-unknown-linux-gnu
The binary will be created at
this over to the remote machine.
On the remote machine, run the
remote-test-server with the
-v for verbose output). Output should look like this:
$ ./remote-test-server -v remote starting test server listening on 0.0.0.0:12345!
You can test if the
remote-test-server is working by connecting to it and
ping\n. It should reply
$ nc $REMOTE_IP 12345 ping pong
To run tests using the remote runner, set the
variable then use
x.py as usual. For example, to run
ui tests for a RISC-V
machine with the IP address
export TEST_DEVICE_ADDR="22.214.171.124:12345" ./x.py test src/test/ui --target riscv64gc-unknown-linux-gnu
remote-test-server was run with the verbose flag, output on the test machine
may look something like
[...] run "/tmp/work/test1007/a" run "/tmp/work/test1008/a" run "/tmp/work/test1009/a" run "/tmp/work/test1010/a" run "/tmp/work/test1011/a" run "/tmp/work/test1012/a" run "/tmp/work/test1013/a" run "/tmp/work/test1014/a" run "/tmp/work/test1015/a" run "/tmp/work/test1016/a" run "/tmp/work/test1017/a" run "/tmp/work/test1018/a" [...]
Tests are built on the machine running
x.py not on the remote machine. Tests
which fail to build unexpectedly (or
ui tests producing incorrect build
output) may fail without ever running on the remote machine.
Some platforms are tested via an emulator for architectures that aren't readily available. For architectures where the standard library is well supported and the host operating system supports TCP/IP networking, see the above instructions for testing on a remote machine (in this case the remote machine is emulated).
There is also a set of tools for orchestrating running the
tests within the emulator. Platforms such as
arm-unknown-linux-gnueabihf are set up to automatically run the tests under
emulation on Travis. The following will take a look at how a target's tests
are run under emulation.
The Docker image for armhf-gnu includes QEMU to emulate the ARM CPU
architecture. Included in the Rust tree are the tools remote-test-client
and remote-test-server which are programs for sending test programs and
libraries to the emulator, and running the tests within the emulator, and
reading the results. The Docker image is set up to launch
remote-test-server and the build tools use
communicate with the server to coordinate running tests (see
TODO: Is there any support for using an iOS emulator?
It's also unclear to me how the wasm or asm.js tests are run.
Crater is a tool for compiling and running tests for every crate on crates.io (and a few on GitHub). It is mainly used for checking for extent of breakage when implementing potentially breaking changes and ensuring lack of breakage by running beta vs stable compiler versions.
You should request a crater run if your PR makes large changes to the compiler or could cause breakage. If you are unsure, feel free to ask your PR's reviewer.
The rust team maintains a few machines that can be used for running crater runs on the changes introduced by a PR. If your PR needs a crater run, leave a comment for the triage team in the PR thread. Please inform the team whether you require a "check-only" crater run, a "build only" crater run, or a "build-and-test" crater run. The difference is primarily in time; the conservative (if you're not sure) option is to go for the build-and-test run. If making changes that will only have an effect at compile-time (e.g., implementing a new trait) then you only need a check run.
Your PR will be enqueued by the triage team and the results will be posted when they are ready. Check runs will take around ~3-4 days, with the other two taking 5-6 days on average.
While crater is really useful, it is also important to be aware of a few caveats:
Not all code is on crates.io! There is a lot of code in repos on GitHub and elsewhere. Also, companies may not wish to publish their code. Thus, a successful crater run is not a magically green light that there will be no breakage; you still need to be careful.
Crater only runs Linux builds on x86_64. Thus, other architectures and platforms are not tested. Critically, this includes Windows.
Many crates are not tested. This could be for a lot of reasons, including that the crate doesn't compile any more (e.g. used old nightly features), has broken or flaky tests, requires network access, or other reasons.
Before crater can be run,
@bors tryneeds to succeed in building artifacts. This means that if your code doesn't compile, you cannot run crater.
A lot of work is put into improving the performance of the compiler and preventing performance regressions. A "perf run" is used to compare the performance of the compiler in different configurations for a large collection of popular crates. Different configurations include "fresh builds", builds with incremental compilation, etc.
The result of a perf run is a comparison between two versions of the compiler (by their commit hashes).
You should request a perf run if your PR may affect performance, especially if it can affect performance adversely.
The following blog posts may also be of interest:
- brson's classic "How Rust is tested"