169 lines
6.4 KiB
Markdown
169 lines
6.4 KiB
Markdown
mutant
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======
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[](http://travis-ci.org/mbj/mutant)
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[](https://gemnasium.com/mbj/mutant)
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[](https://codeclimate.com/github/mbj/mutant)
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[](http://inch-pages.github.io/github/mbj/mutant)
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Mutant is a mutation testing tool for ruby.
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The idea is that if code can be changed and your tests do not notice, either that code isn't being covered
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or it does not have a speced side effect.
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A more readable introduction can be found under: http://solnic.eu/2013/01/23/mutation-testing-with-mutant.html
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Mutant supports MRI and RBX 1.9 and 2.0, while support for jruby is planned.
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It should also work under any ruby engine that supports POSIX-fork(2) semantics.
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Support for MRI 2.1 is unstable, because this MRI release segfaults on basic metaprogramming mutants dependencies do.
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Integrations
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------------
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Only rspec2 and rspec-3 beta2 is supported currently.
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Projects using Mutant
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---------------------
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The following projects adopted mutant, and aim 100% mutation coverage:
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* [axiom](https://github.com/dkubb/axiom)
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* [axiom-types](https://github.com/dkubb/axiom-types)
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* [rom-mapper](https://github.com/rom-rb/rom-mapper)
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* [rom-session](https://github.com/rom-rb/rom-session)
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* [event_bus](https://github.com/kevinrutherford/event_bus)
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* [virtus](https://github.com/solnic/virtus)
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* [quacky](https://github.com/benmoss/quacky)
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* [substation](https://github.com/snusnu/substation)
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* [large_binomials](https://github.com/filipvanlaenen/large_binomials)
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* [promise.rb](https://github.com/lgierth/promise.rb)
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* [full_name](https://github.com/AGILiDEE/full_name)
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* various small/minor stuff under https://github.com/mbj
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Feel free to ping me to add your project to the list!
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Installation
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------------
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Install the gem `mutant` via your preferred method.
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```ruby
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gem install mutant
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```
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If you plan to use the rspec integration you'll have to install `mutant-rspec` also.
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Please add an explicit dependency to `rspec-core` for the rspec version you want to use.
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```ruby
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gem install mutant-rspec
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```
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Mutations
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---------
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Mutant supports a very wide range of mutation operators. Listing them all in detail would blow this document up.
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It is planned to parse a list of mutation operators from the source. In the meantime please refer to the
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[code](https://github.com/mbj/mutant/tree/master/lib/mutant/mutator/node) each subclass of `Mutant::Mutator::Node`
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emits around 3-6 mutations.
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Currently mutant covers the majority of ruby's complex nodes that often occur in method bodies.
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Some stats from the [axiom](https://github.com/dkubb/axiom) library:
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```
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Subjects: 424 # Amount of subjects being mutated (currently only methods)
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Mutations: 6760 # Amount of mutations mutant generated (~13 mutations per method)
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Kills: 6664 # Amount of successfully killed mutations
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Runtime: 5123.13s # Total runtime
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Killtime: 5092.63s # Time spend killing mutations
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Overhead: 0.60%
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Coverage: 98.58% # Coverage score
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Alive: 96 # Amount of alive mutations.
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```
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Nodes still missing a dedicated mutator are handled via the
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[Generic](https://github.com/mbj/mutant/blob/master/lib/mutant/mutator/node/generic.rb) mutator.
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The goal is to remove this mutator and have dedicated mutator for every type of node and removing
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the Generic handler altogether.
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Examples
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--------
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```
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cd virtus
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# Run mutant on virtus namespace
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mutant --include lib --require virtus --use rspec ::Virtus*
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# Run mutant on specific virtus class
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mutant --include lib --require virtus --use rspec ::Virtus::Attribute
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# Run mutant on specific virtus class method
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mutant --include lib --require virtus --use rspec ::Virtus::Attribute.build
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# Run mutant on specific virtus instance method
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mutant --include lib --require virtus --use rspec ::Virtus::Attribute#type
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```
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Presentations:
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--------------
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There are some presentations about mutant in the wild:
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* [Eurocamp-2013](http://2013.eurucamp.org/) / FrOSCon-2013 http://slid.es/markusschirp/mutation-testing
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* [Cologne.rb](http://www.colognerb.de/topics/mutation-testing-mit-mutant) https://github.com/DonSchado/colognerb-on-mutant/blob/master/mutation_testing_slides.pdf
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Subjects:
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---------
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Mutant currently mutates code in instance and singleton methods. It is planned to support mutation
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of constant definitions and domain specific languages, DSL probably as plugins.
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Test-Selection
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--------------
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Mutation testing is slow. The key to making it fast is selecting the correct set of tests to run.
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Mutant currently supports the following built-in strategy for selecting tests/specs:
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Mutant uses the "longest rspec example group descriptions prefix match" to select the tests to run.
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Example for a subject like `Foo::Bar#baz` it will run all example groups with description prefixes in
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`Foo::Bar#baz`, `Foo::Bar` and `Foo`. The order is important, so if mutant finds example groups in the
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current prefix level, these example groups *must* kill the mutation.
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This test selection strategy is compatible with the old `--rspec-dm2` and `--rspec-unit` strategy.
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The old flags were removed. It allows to define very fine grained specs, or coarse grained - as you like.
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Support
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-------
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I'm very happy to receive/answer feedback/questions and critism.
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Your options:
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* GitHub Issues https://github.com/mbj/mutant/issues
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* Ping me on https://twitter.com/_m_b_j_
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* #mutant channel on freenode, I hang around on CET daytimes. (nick mbj)
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You'll also find others [ROM](https://github.com/rom-rb) team members here that can answer questions.
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Credits
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-------
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* [Markus Schirp (mbj)](https://github.com/mbj)
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* A [gist](https://gist.github.com/1065789) from [dkubb](https://github.com/dkubb) showing ideas.
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* Older abandoned [mutant](https://github.com/txus/mutant). For motivating me doing this one.
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* [heckle](https://github.com/seattlerb/heckle). For getting me into mutation testing.
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Contributing
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-------------
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* Fork the project.
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* Make your feature addition or bug fix.
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* Add tests for it. This is important so I don't break it in a
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future version unintentionally.
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* Commit, do not mess with Rakefile or version
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(if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
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* Send me a pull request. Bonus points for topic branches.
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License
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-------
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See LICENSE file.
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