ruby--ruby/spec/rubyspec/core/math/lgamma_spec.rb

require File.expand_path('../../../spec_helper', __FILE__)

describe "Math.lgamma" do
  it "returns [Infinity, 1] when passed 0" do
    Math.lgamma(0).should == [infinity_value, 1]
  end

  platform_is_not :windows do
    it "returns [Infinity, 1] when passed -1" do
      Math.lgamma(-1).should == [infinity_value, 1]
    end
  end

  ruby_version_is "2.4" do
    it "returns [Infinity, -1] when passed -0.0" do
      Math.lgamma(-0.0).should == [infinity_value, -1]
    end
  end

  it "returns [log(sqrt(PI)), 1] when passed 0.5" do
    lg1 = Math.lgamma(0.5)
    lg1[0].should be_close(Math.log(Math.sqrt(Math::PI)), TOLERANCE)
    lg1[1].should == 1
  end

  it "returns [log(2/3*PI, 1] when passed 6.0" do
    lg2 = Math.lgamma(6.0)
    lg2[0].should be_close(Math.log(120.0), TOLERANCE)
    lg2[1].should == 1
  end

  it "returns an approximate value when passed -0.5" do
    lg1 = Math.lgamma(-0.5)
    lg1[0].should be_close(1.2655121, TOLERANCE)
    lg1[1].should == -1
  end

  it "returns an approximate value when passed -1.5" do
    lg2 = Math.lgamma(-1.5)
    lg2[0].should be_close(0.8600470, TOLERANCE)
    lg2[1].should == 1
  end

  it "raises Math::DomainError when passed -Infinity" do
    lambda { Math.lgamma(-infinity_value) }.should raise_error(Math::DomainError)
  end

  it "returns [Infinity, 1] when passed Infinity" do
    Math.lgamma(infinity_value).should == [infinity_value, 1]
  end

  it "returns [NaN, 1] when passed NaN" do
    Math.lgamma(nan_value)[0].nan?.should be_true
    Math.lgamma(nan_value)[1].should == 1
  end
end