Change location of concurrency docs

This commit is contained in:
Markus Schirp 2018-11-27 13:07:46 +00:00
parent 1b65924e73
commit 27acea588e
2 changed files with 40 additions and 21 deletions

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@ -24,6 +24,7 @@ Topics
* [Reading Reports](/docs/reading-reports.md) * [Reading Reports](/docs/reading-reports.md)
* [Known Problems](/docs/known-problems.md) * [Known Problems](/docs/known-problems.md)
* [Limitations](/docs/limitations.md) * [Limitations](/docs/limitations.md)
* [Concurrency](/docs/concurrency.md)
Sponsoring Sponsoring
---------- ----------
@ -97,27 +98,6 @@ Example for a subject like `Foo::Bar#baz` it will run all example groups with de
current prefix level, these example groups *must* kill the mutation. current prefix level, these example groups *must* kill the mutation.
Concurrency
-----------
By default, mutant will test mutations in parallel by running up to one process for each core on your system. You can control the number of processes created using the `--jobs` argument.
Mutant forks a new process for each mutation to be tested to prevent side affects in your specs and the lack of thread safety in rspec from impacting the results.
If the code under test relies on a database, you may experience problems when running mutant because of conflicting data in the database. For example, if you have a test like this:
```
m = MyModel.create!(...)
expect(MyModel.first.name).to eql(m.name)
```
It might fail if some other test wrote a record to the MyModel table at the same time as this test was executed. (It would find the MyModel record created by the other test.) Most of these issues can be fixed by writing more specific tests. Here is a concurrent safe version of the same test:
```
m = MyModel.create!(...)
expect(MyModel.find_by_id(m.id).name).to eql(m.name)
```
You may also try wrapping your test runs in transactions.
Note that some databases, SQLite in particular, are not designed for concurrent access and will fail if used in this manner. If you are using SQLite, you should set the `--jobs` to 1.
Neutral (noop) Tests Neutral (noop) Tests
-------------------- --------------------

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