Merge pull request #6 from nisshiee/readme

Write README

Author: nisshiee

README.md

@@ -2,9 +2,22 @@
 
 [![Build Status](https://travis-ci.org/nisshiee/validation_examples_matcher.svg?branch=master)](https://travis-ci.org/nisshiee/validation_examples_matcher)
 
-Welcome to your new gem! In this directory, you'll find the files you need to be able to package up your Ruby library into a gem. Put your Ruby code in the file `lib/validation_examples_matcher`. To experiment with that code, run `bin/console` for an interactive prompt.
+ValidationExamplesMatcher supports writing rails model's validation specs.
 
-TODO: Delete this and the text above, and describe your gem
+e.g.
+
+```ruby
+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.
 
 ## Installation
 
@@ -18,26 +31,67 @@ And then execute:
 
     $ bundle
 
-Or install it yourself as:
+## Usage
 
-    $ gem install validation_examples_matcher
+Let me show how to use ValidationExamplesMatcher in case of following model.
 
-## Usage
+```ruby
+class MyModel < ActiveRecord::Base
+  validates :name, presence: true
+  validates :name, length: { maxmum: 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](https://github.com/thoughtbot/factory_girl) is very nice.
+
+```ruby
+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.
 
-TODO: Write usage instructions here
+```ruby
+RSpec.define MyModel do
+  subject { FactoryGirl.build(:my_model) }
 
-## Development
+  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
+```
 
-After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.
+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.
 
-To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).
+`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.
+
+```ruby
+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
+```
 
 ## Contributing
 
-Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/validation_examples_matcher.
+Bug reports and pull requests are welcome on GitHub at https://github.com/nisshiee/validation_examples_matcher.
 
 
 ## License
 
 The gem is available as open source under the terms of the [MIT License](http://opensource.org/licenses/MIT).
-