01 example_spec.rb

require 'rspec'

describe "Behaviour" do
  it "should pass" do
    true.should eq true
  end

  it "should fail" do
    true.should eq false
  end

  it "should pending"
end

02 rspec_runner.rb

require 'rspec'
require 'rspec/core/formatters/json_formatter'

config = RSpec.configuration
json_formatter = RSpec::Core::Formatters::JsonFormatter.new(config.out)

# create reporter with json formatter
reporter =  RSpec::Core::Reporter.new(json_formatter)
# set reporter for rspec configuration
config.instance_variable_set(:@reporter, reporter)

# execute rspec runner
# 'example_spec.rb' is the location of the spec file
RSpec::Core::Runner.run(['example_spec.rb'])

# output test result as json
# see example output in `rspec_json_formatter_result.rb`
puts json_formatter.output_hash

03 rspec_json_formatter_result.rb

{
  :examples => [
    {
      :description => "should pass",
      :full_description => "Behaviour should pass",
      :status => "passed",
      :file_path => "./my_spec.rb",
      :line_number => 4
    }, 
    {
      :description => "should fail",
      :full_description => "Behaviour should fail",
      :status => "failed",
      :file_path => "./my_spec.rb",
      :line_number => 8,
      :exception => 
        {
          :class => "RSpec::Expectations::ExpectationNotMetError",
          :message => "\nexpected:false\n     got:true\n\n(compared using ==)\n",
          :backtrace => ["/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-expectations-2.12.1/lib/rspec/expectations/fail_with.rb:33:in `fail_with'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-expectations-2.12.1/lib/rspec/expectations/handler.rb:31:in `handle_matcher'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-expectations-2.12.1/lib/rspec/expectations/syntax.rb:53:in `should'", "/Users/jing/Documents/other/test/my_spec.rb:9:in `block (2 levels) in <top (required)>'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/example.rb:114:in `instance_eval'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/example.rb:114:in `block in run'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/example.rb:254:in `with_around_each_hooks'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/example.rb:111:in `run'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/example_group.rb:388:in `block in run_examples'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/example_group.rb:384:in `map'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/example_group.rb:384:in `run_examples'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/example_group.rb:369:in `run'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/command_line.rb:28:in `block (2 levels) in run'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/command_line.rb:28:in `map'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/command_line.rb:28:in `block in run'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/reporter.rb:34:in `report'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/command_line.rb:25:in `run'", "/Users/jing/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/rspec-core-2.12.2/lib/rspec/core/runner.rb:80:in `run'", "runner.rb:19:in `<main>'"]
        }
    }, 
    {
      :description => "should pending",
      :full_description => "Behaviour should pending",
      :status => "pending",
      :file_path => "./my_spec.rb",
      :line_number => 12
    }
  ],
  
  :summary => {
    :duration => 0.001543,
    :example_count => 3,
    :failure_count => 1,
    :pending_count => 1
  },
  
  :summary_line => "3 examples, 1 failure, 1 pending"
}