require File.expand_path(File.dirname(__FILE__) + '/../../spec_helper')

include Fathom::Distributions

describe Gaussian do
  
  before do
    @opts = {:mean => 0, :sd => 0.1, :confidence_interval => 0.05}
  end
  
  it "should provide a GSL::Rng through rng" do
    Gaussian.rng.should be_a(GSL::Rng)
  end
  
  it "should be able to generate a random variable through GSL::Rng#gaussian" do
    Gaussian.rng.should_receive(:gaussian).and_return(0.5)
    Gaussian.rand(1)
  end
  
  it "should be able to generate an inverse CDF" do
    Gaussian.inverse_cdf(@opts).should be_close(-0.16448, 0.00001)
  end
  
  it "should require mean as an option for an inverse CDF" do
    @opts.delete(:mean)
    lambda{Gaussian.inverse_cdf(@opts)}.should raise_error
  end
  
  it "should require a Gaussian deviation for an inverse CDF" do
    @opts.delete(:sd)
    lambda{Gaussian.inverse_cdf(@opts)}.should raise_error
  end
  
  it "should take std as an alias for sd when creating an inverse CDF" do
    @opts.delete(:sd)
    Gaussian.inverse_cdf(@opts.merge(:std => 0.1)).should be_close(-0.16448, 0.00001)
  end

  it "should take standard_deviation as an alias for sd when creating an inverse CDF" do
    @opts.delete(:sd)
    Gaussian.inverse_cdf(@opts.merge(:standard_deviation => 0.1)).should be_close(-0.16448, 0.00001)
  end
  
  it "should be able to set upper to true and get Q instead of P" do
    Gaussian.inverse_cdf(@opts.merge(:upper =>true)).should be_close(0.16448, 0.00001)
  end
  
  it "should be able to take a different confidence interval" do
    Gaussian.inverse_cdf(@opts.merge(:confidence_interval => 0.1)).should be_close(-0.12815, 0.00001)
  end

  it "should have a lower_bound alias for inverse_cdf" do
    Gaussian.lower_bound(@opts).should eql(Gaussian.inverse_cdf(@opts))
  end
  
  it "should have an upper_bound shortcut for inverse_cdf(:upper => true, ...)" do
    Gaussian.upper_bound(@opts).should eql(Gaussian.inverse_cdf(@opts.merge(:upper => true)))
  end
  
  it "should provide interval values, an array of the lower and upper bounds" do
    Gaussian.interval_values(@opts.merge(:confidence_interval => 0.9)).should eql([Gaussian.lower_bound(@opts), Gaussian.upper_bound(@opts)])
  end
end