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mrubyc-test is an unit test framework for mruby/c, supporting basic assertions, stub and mock.


The API design and implementation of this gem is greatly inspired by test-unit. Thank the great work.


  • Tests are applicable to class and its instance methods written with mruby
  • C code will not be covered directly though, you can test your C implementation if you write mruby wrapper class. In this case, your test class (it also written with mruby) will test an integrated circumstance of C and mruby
  • Tests will run on your PC (POSIX) hereby you can write business logic with mruby/c apart from C API matters like microcontroler peripherals
  • Simple assertions ... enough for almost firmware development though, I will increase the number of assertion
  • Stub ... You can write your mruby code without peripheral implementation by C
  • Mock ... You can call any method still doesn't exist
  • The implementation of your application and test code will be analyzed by CRuby program, then comlpiled into mruby byte code and executed on mruby/c VM


Add this line to your application's Gemfile:

gem 'mrubyc-test'

And then execute:

$ bundle

Or install it yourself as:

$ gem install mrubyc-test


Assuming you are using mrubyc-utils to manage your project and rbenv to manage Ruby versions. It means you have .mrubycconfig and .ruby-version in the top directory of your project.

Besides, you have to locate mruby model files that are the target of testing like mrblib/models/class_name.rb

And read here about why you should use mrubyc-utils.

This is an example of ESP32 project:

~/your_project $ tree
├── .mrubycconfig               # Created by mrubyc-utils
├── .ruby-version               # It should be mruby's version something like 'mruby-1.4.1'
├── Makefile
├── build
├── components
├── main
├── mrblib
│      └── models               # Place your model class files here
│            ├── class_name.rb  # The testing target `ClassName`
│            └── my_class.rb    # The testing target `MyClass`
│      └── loops
│            ├── main.rb        # Loop script isn't covered by mrubyc-test. use mrubyc-debugger
│            └── sub.rb         # Loop script isn't covered by mrubyc-test. use mrubyc-debugger
└── sdkconfig

In the same directory:

$ mrubyc-utils test init

Then, some directories and files will be created in your project. Now you can run test because a sample test code was also created.

$ mrubyc-utils test

You should get some assertion failures. Take a look at test/sample_test.rb to handle the failures and find how to write your own test.


def assertions
  my_var = 1
  assert_equal     1, my_var  # => success
  assert_not_equal 2, my_var  # => success
  assert_not_nil   my_var     # => success


Assuming you have a model file at mrblib/models/sample.rb

class Sample
  attr_accessor :result
  def do_something(arg)
    @result = arg + still_not_defined_method

Then you can test #do_something method without having #still_not_defind_method like this:

def stub_case
  sample_obj =
  stub(sample_obj).still_not_defined_method { ", so we are nice" }
  sample_obj.do_something("Ruby is nice")
  assert_equal 'Ruby is nice, so we are nice', sample_obj.result


mrblib/models/sample.rb looks like this time:

class Sample
  def do_other_thing

You can test whether #is_to_be_hit method will be called:

def mock_case
  sample_obj =

Known problems

  • You have to write stub or mock test fot all the methods still do not exist otherwise your test won't turn green

TODO (possibly)

  • Assertion against arguments of mock
  • Other assertions like LT(<), GTE(>=), include?, ...etc.
  • bla bla bla


Bug reports and pull requests are welcome on GitHub at This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the The 3-Clause BSD License.

Code of Conduct

Everyone interacting in the Mrubyc::Test project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.

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