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Auto merge of #2811 - saethlin:readme-nextest, r=RalfJung

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Add a section on using nextest

Inspired by this question: https://github.com/rust-lang/miri/issues/2805
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bors 2023-03-12 21:23:24 +00:00
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src/tools/miri/README.md
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@ -225,6 +225,26 @@ degree documented below):
reduced feature set. We might ship Miri with a nightly even when some features
on these targets regress.
### Running tests in parallel
Though it implements Rust threading, Miri itself is a single-threaded interpreter.
This means that when running `cargo miri test`, you will probably see a dramatic
increase in the amount of time it takes to run your whole test suite due to the
inherent interpreter slowdown and a loss of parallelism.
You can get your test suite's parallelism back by running `cargo miri nextest run -jN`
(note that you will need [`cargo-nextest`](https://nexte.st) installed).
This works because `cargo-nextest` collects a list of all tests then launches a
separate `cargo miri run` for each test. You will need to specify a `-j` or `--test-threads`;
by default `cargo miri nextest run` runs one test at a time. For more details, see the
[`cargo-nextest` Miri documentation](https://nexte.st/book/miri.html).
Note: This one-test-per-process model means that `cargo miri test` is able to detect data
races where two tests race on a shared resource, but `cargo miri nextest run` will not detect
such races.
Note: `cargo-nextest` does not support doctests, see https://github.com/nextest-rs/nextest/issues/16
### Common Problems
When using the above instructions, you may encounter a number of confusing compiler