40 lines
1.3 KiB
Markdown
40 lines
1.3 KiB
Markdown
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Concurrency
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===========
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By default, mutant will test mutations in parallel by running up
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to one process for each core on your system. You can control the
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number of processes created using the `-j/--jobs` argument.
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Mutant forks a new process for each mutation to be tested to prevent side
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affects in your specs and the lack of thread safety in integrations from
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impacting the results.
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Database
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--------
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If the code under test relies on a database, you may experience problems
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when running mutant because of conflicting data in the database. For
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example, if you have a test like this:
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```ruby
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resource = MyModel.create!(...)
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expect(MyModel.first.name).to eql(resource.name)
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```
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It might fail if some other test wrote a record to the `MyModel` table
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at the same time as this test was executed. (It would find the MyModel
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record created by the other test.) Most of these issues can be fixed
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by writing more specific tests. Here is a concurrent safe version of
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the same test:
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```
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resource = MyModel.create!(...)
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expect(MyModel.find_by_id(m.id).name).to eql(resource.name)
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```
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An alternative is to try wrapping each test into an enclosing transaction.
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Note that some databases, SQLite in particular, are not designed for
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concurrent access and will fail if used in this manner. If you are
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using SQLite, you should set the `--jobs` to 1.
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