183 lines
6.2 KiB
Markdown
183 lines
6.2 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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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. It should also work under
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any ruby engine that supports POSIX-fork(2) semantics.
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Only rspec2 is supported currently. This is subject to change.
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It is easy to write a mutation killer for other test/spec frameworks than rspec2.
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Just create your own Mutant::Killer subclass, and make sure I get a PR!
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See this [ASCII-Cast](http://ascii.io/a/1707) for mutant in action! (v0.2.1)
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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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* 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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The 0.2 series is stable but has outdated dependencies. The 0.3 series is in beta phase currently.
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```ruby
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gem install mutant --pre
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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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A some stats from the [axiom](https://github.com/dkubb/axiom) library:
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```
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Subjects: 417 # Amount of subjects being mutated (currently only methods)
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Mutations: 5442 # Amount of mutations mutant generated (~13 mutations per method)
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Kills: 5385 # Amount of successfully killed mutations
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Runtime: 1898.11s # Total runtime
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Killtime: 1884.17s # Time spend killing mutations
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Overhead: 0.73%
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Coverage: 98.95% # Coverage score
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Alive: 57 # 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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CLI will be simplified in the next releases, but currently stick with this:
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```
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cd virtus
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# Run mutant on virtus namespace (that uses the dm-2 style spec layout)
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mutant --rspec-dm2 '::Virtus*'
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# Run mutant on specific virtus class
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mutant --rspec-dm2 ::Virtus::Attribute
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# Run mutant on specific virtus class method
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mutant --rspec-dm2 ::Virtus::Attribute.build
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# Run mutant on specific virtus instance method
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mutant --rspec-dm2 ::Virtus::Attribute#name
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```
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Strategies
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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 strategies for selecting tests/specs.
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### --rspec-dm2
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This strategy is the *fastest* but requires discipline in spec file naming.
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The following specs are executed to kill a mutation on:
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```
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Public instance methods: spec/unit/#{namespace}/#{class_name}/#{method_name}_spec.rb
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Public singleton methods: spec/unit/#{namespace}/#{class_name}/class_methods/#{method_name}_spec.rb
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Private instance methods: spec/unit/#{namespace}/#{class_name}/*_spec.rb
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Private singleton methods: spec/unit/#{namespace}/#{class_name}/class_methods/*_spec.rb
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```
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#### Expansions:
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Symbolic operator-like methods are expanded, e.g. ```Foo#<<``` is expanded to:
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```
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spec/unit/foo/left_shift_operator_spec.rb
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````
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The full list of expansions can be found here:
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https://github.com/mbj/mutant/blob/master/lib/mutant/constants.rb
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### --rspec-unit
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This strategy executes all specs under ``./spec/unit`` for each mutation.
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### --rspec-integration
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This strategy executes all specs under ``./spec/integration`` for each mutation.
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### --rspec-full
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This strategy executes all specs under ``./spec`` for each mutation.
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In the future, we plan on allowing explicit selections on the specs to be run, as well as support for other test frameworks.
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Custom project specific strategies are also on the roadmap.
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Alternatives
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------------
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* [heckle](https://github.com/seattlerb/heckle)
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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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* #rom-rb channel on freenode, I hang around on CET daytimes. (nick mbj)
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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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