RSpec clone

A minimalist RSpec clone with all the essentials.

What did you RSpec?

Status

Home Version Yard documentation Ruby RuboCop License

Project Goals

  1. Maintain low code complexity to avoid false negatives and false positives.
  2. Implement the loading of specifications using simple, atomic, and thread-safe Ruby primitives.
  3. Avoid cluttering the interface with unnecessary alternative syntaxes.
  4. Provide the basics of the RSpec DSL for writing tests.

Some Differences

  • Monkey-patching is not an available option.
  • The framework does not use hacks such as the at_exit hook to trigger tests.
  • Malicious actual values cannot compromise results.
  • If no subject is explicitly determined, it remains undefined.
  • If no described class is set, described_class is undefined rather than nil.
  • Expectations cannot be added inside a before block.
  • Arbitrary helper methods are not accessible within examples.
  • The let method defines a helper method rather than a memoized helper method.
  • The one-liner is_expected syntax is compatible with block expectations.
  • Definitions of subject, before, and let must precede examples.
  • The after hook is unsupported.
  • The execution of the test suite halts immediately when an error is detected.
  • Each context block isolates its tests and any potential side effects.
  • The its method is available without the need for external dependencies.

Installation

Add this line to your application's Gemfile:

gem "r_spec-clone"

And then execute:

bundle install

Or install it yourself as:

gem install r_spec-clone

Overview

RSpec clone provides a structure for writing executable examples of how your code should behave.

Inspired by RSpec, it includes a domain-specific language (DSL) that allows you to write examples in a way similar to plain english.

A basic spec looks something like this:

RSpec clone demo

Usage

Anatomy of a Spec File

To utilize the RSpec module and its DSL, include require "r_spec" in your spec files. Many projects organize these includes through a custom spec helper.

Concrete test cases are defined in it blocks. An optional (but recommended) descriptive string or module indicates the purpose of the test and a block contains the main logic of the test.

Test cases that have been defined or outlined but are not yet expected to work can be defined using pending instead of it. They will not be run but show up in the spec report as pending.

An it block contains an example that should invoke the code to be tested and define what is expected of it. Each example can contain multiple expectations, but it should test only one specific behaviour.

The its method can also be used to generate a nested example group with a single example that specifies the expected value (or the block expectations) of an attribute of the subject using is_expected.

To express an expectation, wrap an object or block in expect, call to (or not_to) and pass it a matcher object. If the expectation is met, code execution continues. Otherwise the example has failed and other code will not be executed.

In test files, specs can be structured by example groups which are defined by describe and context sections. Typically a top level describe defines the outer unit (such as a class) to be tested by the spec. Further describe sections can be nested within the outer unit to specify smaller units under test (such as individual methods).

For unit tests, it is recommended to follow the conventions for method names:

  • outer describe is the name of the class, inner describe targets methods;
  • instance methods are prefixed with #, class methods with ..

To establish certain contexts — think empty array versus array with elements — the context method may be used to communicate this to the reader.

Unlike a describe block, all specifications executed within a context are isolated in a subprocess. This prevents possible side effects on the Ruby object environment from being propagated outside their context, which could alter the result of the unit test suite.

Note: if you are wondering what kind of code might be generated by the DSL, an article that shows the dynamic transcription of the main methods with simple examples is available in Chinese, in English and in Japanese.

Expectations

Expectations define if the value being tested (actual) matches a certain value or specific criteria.

Equivalence

expect(actual).to eql(expected) # passes if expected.eql?(actual)
expect(actual).to eq(expected)  # passes if expected.eql?(actual)

Identity

expect(actual).to equal(expected) # passes if expected.equal?(actual)
expect(actual).to be(expected)    # passes if expected.equal?(actual)

Comparisons

expect(actual).to be_within(delta).of(expected) # passes if (expected - actual).abs <= delta

Regular expressions

expect(actual).to match(expected) # passes if expected.match?(actual)

Expecting errors

expect { actual }.to raise_exception(expected) # passes if expected exception is raised

True

expect(actual).to be_true # passes if true.equal?(actual)

False

expect(actual).to be_false # passes if false.equal?(actual)

Nil

expect(actual).to be_nil # passes if nil.equal?(actual)

Type/class

expect(actual).to be_instance_of(expected)    # passes if expected.equal?(actual.class)
expect(actual).to be_an_instance_of(expected) # passes if expected.equal?(actual.class)

Predicate

expect(actual).to be_xxx            # passes if actual.xxx?
expect(actual).to be_have_xxx(:yyy) # passes if actual.has_xxx?(:yyy)
Examples
expect([]).to be_empty
expect(foo: 1).to have_key(:foo)

Change

expect { object.action }.to change(object, :value).to(new)
expect { object.action }.to change(object, :value).from(old).to(new)
expect { object.action }.to change(object, :value).by(delta)
expect { object.action }.to change(object, :value).by_at_least(minimum_delta)
expect { object.action }.to change(object, :value).by_at_most(maximum_delta)

Satisfy

expect(actual).to(satisfy { |value| value == expected })

Running specs

By convention, specs live in the spec/ directory of a project. Spec files should end with _spec.rb to be recognizable as such.

Depending of the project settings, you may run the specs of a project by running rake spec (see Rake integration example section below). A single file can also be executed directly with the Ruby interpreter.

Examples

Run all specs in files matching spec/**/*_spec.rb:

bundle exec rake spec

Run a single file:

ruby spec/my/test/file_spec.rb

It is not recommended, but the RSpec's rspec command line might also work:

rspec spec/my/test/file_spec.rb
rspec spec/my/test/file_spec.rb:42
rspec spec/my/test/
rspec

Spec helper

Many projects use a custom spec helper file, usually named spec/spec_helper.rb.

This file is used to require r_spec/clone and other includes, like the code from the project needed for every spec file.

Rake integration example

The following Rakefile settings should be enough:

require "bundler/gem_tasks"
require "rake/testtask"

Rake::TestTask.new do |t|
  t.pattern = "spec/**/*_spec.rb"
end

task spec: :test
task default: :test

And then execute:

bundle exec rake

Performance

The benchmarks compare the performance of r_spec-clone with the following frameworks (in alphabetical order):

Boot time

Benchmark against 100 executions of a file containing 1 expectation (lower is better).

Boot time benchmark

Runtime

Benchmark against 1 execution of a file containing 100,000 expectations (lower is better).

Runtime benchmark

Test suite

RSpec clone's specifications are self-described here: spec/

Contact

Special thanks ❤️

I would like to thank the whole RSpec team for all their work. It's a great framework and it's a pleasure to work with every day.

Without RSpec, this clone would not have been possible.

Buy me a coffee ☕

If you like this project, please consider making a small donation.

Donate

Versioning

RSpec clone follows Semantic Versioning 2.0.

License

The gem is available as open source under the terms of the MIT License.

One more thing

Under the hood, RSpec clone is largely animated by a collection of testing libraries designed to make programmers happy.

It's a living example of what we can do combining small libraries together that can boost the fun of programming.

Fix testing tools logo for Ruby