Running tests

You can run the tests using x.py. The most basic command – which you will almost never want to use! – is as follows:

> ./x.py test

This will build the full stage 2 compiler and then run the whole test suite. You probably don't want to do this very often, because it takes a very long time, and anyway bors / travis will do it for you. (Often, I will run this command in the background after opening a PR that I think is done, but rarely otherwise. -nmatsakis)

The test results are cached and previously successful tests are ignored during testing. The stdout/stderr contents as well as a timestamp file for every test can be found under build/ARCH/test/. To force-rerun a test (e.g. in case the test runner fails to notice a change) you can simply remove the timestamp file.

Note that some tests require a Python-enabled gdb. You can test if your gdb install supports Python by using the python command from within gdb. Once invoked you can type some Python code (e.g. print("hi")) followed by return and then CTRL+D to execute it. If you are building gdb from source, you will need to configure with --with-python=<path-to-python-binary>.

Running a subset of the test suites

When working on a specific PR, you will usually want to run a smaller set of tests, and with a stage 1 build. For example, a good "smoke test" that can be used after modifying rustc to see if things are generally working correctly would be the following:

> ./x.py test --stage 1 src/test/{ui,compile-fail,run-pass}

This will run the ui, compile-fail, and run-pass test suites, and only with the stage 1 build. Of course, the choice of test suites is somewhat arbitrary, and may not suit the task you are doing. For example, if you are hacking on debuginfo, you may be better off with the debuginfo test suite:

> ./x.py test --stage 1 src/test/debuginfo

Run only the tidy script

> ./x.py test src/tools/tidy

Run tests on the standard library

> ./x.py test src/libstd

Run tests on the standard library and run the tidy script

> ./x.py test src/libstd src/tools/tidy

Run tests on the standard library using a stage 1 compiler

>   ./x.py test src/libstd --stage 1

By listing which test suites you want to run you avoid having to run tests for components you did not change at all.

Warning: Note that bors only runs the tests with the full stage 2 build; therefore, while the tests usually work fine with stage 1, there are some limitations. In particular, the stage1 compiler doesn't work well with procedural macros or custom derive tests.

Running an individual test

Another common thing that people want to do is to run an individual test, often the test they are trying to fix. One way to do this is to invoke x.py with the --test-args option:

> ./x.py test --stage 1 src/test/ui --test-args issue-1234

Under the hood, the test runner invokes the standard rust test runner (the same one you get with #[test]), so this command would wind up filtering for tests that include "issue-1234" in the name.

Using incremental compilation

You can further enable the --incremental flag to save additional time in subsequent rebuilds:

> ./x.py test --stage 1 src/test/ui --incremental --test-args issue-1234

If you don't want to include the flag with every command, you can enable it in the config.toml, too:

# Whether to always use incremental compilation when building rustc
incremental = true

Note that incremental compilation will use more disk space than usual. If disk space is a concern for you, you might want to check the size of the build directory from time to time.

Running tests manually

Sometimes it's easier and faster to just run the test by hand. Most tests are just rs files, so you can do something like

> rustc +stage1 src/test/ui/issue-1234.rs

This is much faster, but doesn't always work. For example, some tests include directives that specify specific compiler flags, or which rely on other crates, and they may not run the same without those options.