Using Rspec DescribeMethod

Using Rspec DescribeMethod is super simple.

In your Gemfile:

group :development, :testing do
  gem 'rspec-describe-method'
end

In your spec_helper.rb:

require 'rspec/describe-method'

And your specs can look like this:

describe String do
    describe_method '.new' do
        it{ should be_a String }
    end

    describe_method '#concat', 'argument' do
        it{ should match /argument/i }
    end

    context 'with an instance' do
        subject{ String.new 'test' }

        describe_method '#upcase' do
            it{ should eq 'TEST' }
        end
    end
end

So what's happening behind the scenes?

Essentially we do a little bit of meta-programming and replace the describe_method with a normal describe and subject call as so:

describe User do
    #--- This... ---------------

    describe_method '#to_s' do
        it{ should be_a String }
    end

    #--- Is Equivalent to... ---

    describe '#to_s' do
        subject{ described_class.new.to_s }

        it{ should be_a String }
    end
end

describe User do
    subject( :instance ){ described_class.new }

    #--- This... ----------------

    describe_method '.find', 1 do
        it{ should be_a User }
    end

    #--- Is Equivalent to... ----

    describe '.find( 1 )' do
        subject{ instance.class.find 1 }

        it{ should be_a String )
    end
end

Describe a method call on the current test subject in your specs with 'describe_method', and a # for instance methods and a . for class methods.

Instances will automatically delagate to their class, and classes will automatically create an instance of themselves.

Alias method: when_calling

The alias method when_calling is provided which makes specs more human-readable, especially when calls are nested within eachother:

describe String do
    subject{ String.new 'test' }

    when_calling '#upcase' {
        it{ should eq 'TEST' }

        when_calling '#+', 'ING' {
            it{ should eq 'TESTING' }
        }
    }
end

NOTE

When the subject is a Class, and you call an instance method describe_method "#something" the class will call .new on itself with NO ARGUMENTS, you may not want this behavior.