45 lines
2 KiB
Markdown
45 lines
2 KiB
Markdown
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Known Problems
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==============
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Mutations with Infinite Runtimes
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---------------------------------
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Occasionally mutant will produce a mutation with an infinite runtime. When this happens
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mutant will look like it is running indefinitely without killing a remaining mutation. To
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avoid mutations like this, consider adding a timeout around your tests. For example, in
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RSpec you can add the following to your `spec_helper`:
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```ruby
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config.around(:each) do |example|
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Timeout.timeout(5, &example)
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end
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```
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which will fail specs which run for longer than 5 seconds.
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The Crash / Stuck Problem (MRI)
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-------------------------------
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Mutations generated by mutant can cause MRI to enter VM states its not prepared for.
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All MRI versions > 1.9 and < 2.2.1 are affected by this depending on your compiler flags,
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compiler version, and OS scheduling behavior.
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This can have the following unintended effects:
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* MRI crashes with a segfault. Mutant kills each mutation in a dedicated fork to isolate
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the mutations side effects when this fork terminates abnormally (segfault) mutant
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counts the mutation as killed.
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* MRI crashes with a segfault and gets stuck when handling the segfault.
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Depending on the number of active kill jobs mutant might appear to continue normally until
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all workers are stuck into this state when it begins to hang.
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Currently mutant must assume that your test suite simply not terminated yet as from the outside
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(parent process) the difference between a long running test and a stuck MRI is not observable.
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Its planned to implement a timeout enforced from the parent process, but ideally MRI simply gets fixed.
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References:
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* [MRI fix](https://github.com/ruby/ruby/commit/8fe95fea9d238a6deb70c8953ceb3a28a67f4636)
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* [MRI backport to 2.2.1](https://github.com/ruby/ruby/commit/8fe95fea9d238a6deb70c8953ceb3a28a67f4636)
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* [Mutant issue](https://github.com/mbj/mutant/issues/265)
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* [Upstream bug redmine](https://bugs.ruby-lang.org/issues/10460)
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* [Upstream bug github](https://github.com/ruby/ruby/pull/822)
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