ValidationExamplesMatcher supports writing rails model's validation specs.

e.g.

RSpec.describe MyModel do
  ...

  it { is_expected.to be_invalid_on(:name).with(nil) }
  it { is_expected.to be_invalid_on(:name).with('') }
  it { is_expected.to be_valid_on(:name).with('my name') }
end

ValidationExamplesMatcher sets a particular value ― nil, empty string and 'my name' ― actually. Then the matcher calls valid? or invalid? method and checks results of validation.

Add this line to your application's Gemfile:

gem 'validation_examples_matcher'

And then execute:

$ bundle

Let me show how to use ValidationExamplesMatcher in case of following model.

class MyModel < ActiveRecord::Base
  validates :name, presence: true
  validates :name, length: { maximum: 4 }, on: :create
end

First, you have to define subject as target model object. It's good to define it as valid object. Creating object with factory_girl is very nice.

RSpec.define MyModel do
  subject { FactoryGirl.build(:my_model) }
  # subject { MyModel.new } => also ok but not recommended
end

Second, write invalid case examples and valid case examples using ValidationExamplesMatcher. In case of MyModel, :name attribute is invalid when its' value is nil or empty string. 'my name' is typical valid example.

RSpec.define MyModel do
  subject { FactoryGirl.build(:my_model) }

  it { is_expected.to be_invalid_on(:name).with(nil) }
  it { is_expected.to be_invalid_on(:name).with('') }
  it { is_expected.to be_valid_on(:name).with('my name') }
end

Arguments of be_invalid_on or be_valid_on indicate attribute name. And arguments of with chain is a value which will be set to the attribute.

ActiveModel::Validations can define validations on specific contexts. MyModel has length validation only on :create context. You can also define validation spec for such case using on_context chain.

RSpec.define MyModel do
  subject { FactoryGirl.build(:my_model) }

  it { is_expected.to be_invalid_on(:name).with(nil) }
  it { is_expected.to be_invalid_on(:name).with('') }
  it { is_expected.to be_valid_on(:name).with('my name') }

  it { is_expected.to be_valid_on(:name).with('4cha').on_context(:create) }
  it { is_expected.to be_invalid_on(:name).with('5char').on_context(:create) }
end

see CHANGELOG.md

Bug reports and pull requests are welcome on GitHub at https://github.com/speee/validation_examples_matcher.

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