Add be_positive_zero and be_negative_zero matchers

mspec/lib/mspec/matchers.rb

@@ -32,3 +32,4 @@
 require 'mspec/matchers/output'
 require 'mspec/matchers/output_to_fd'
 require 'mspec/matchers/respond_to'
+require 'mspec/matchers/signed_zero'

mspec/lib/mspec/matchers/signed_zero.rb

@@ -0,0 +1,28 @@
+class SignedZeroMatcher
+  def initialize(expected_sign)
+    @expected_sign = expected_sign
+  end
+
+  def matches?(actual)
+    @actual = actual
+    (1.0/actual).infinite? == @expected_sign
+  end
+
+  def failure_message
+    ["Expected #{@actual}", "to be #{"-" if @expected_sign == -1}0.0"]
+  end
+
+  def negative_failure_message
+    ["Expected #{@actual}", "not to be #{"-" if @expected_sign == -1}0.0"]
+  end
+end
+
+class Object
+  def be_positive_zero
+    SignedZeroMatcher.new(1)
+  end
+
+  def be_negative_zero
+    SignedZeroMatcher.new(-1)
+  end
+end

mspec/spec/matchers/signed_zero_spec.rb

@@ -0,0 +1,32 @@
+require File.dirname(__FILE__) + '/../spec_helper'
+require 'mspec/expectations/expectations'
+require 'mspec/matchers/signed_zero'
+
+describe SignedZeroMatcher do
+  it "matches when actual is zero and has the correct sign" do
+    SignedZeroMatcher.new(1).matches?(0.0).should == true
+    SignedZeroMatcher.new(-1).matches?(-0.0).should == true
+  end
+
+  it "does not match when actual is non-zero" do
+    SignedZeroMatcher.new(1).matches?(1.0).should == false
+    SignedZeroMatcher.new(-1).matches?(-1.0).should == false
+  end
+
+  it "does not match when actual is zero but has the incorrect sign" do
+    SignedZeroMatcher.new(1).matches?(-0.0).should == false
+    SignedZeroMatcher.new(-1).matches?(0.0).should == false
+  end
+
+  it "provides a useful failure message" do
+    matcher = SignedZeroMatcher.new(-1)
+    matcher.matches?(0.0)
+    matcher.failure_message.should == ["Expected 0.0", "to be -0.0"]
+  end
+
+  it "provides a useful negative failure message" do
+    matcher = SignedZeroMatcher.new(-1)
+    matcher.matches?(-0.0)
+    matcher.negative_failure_message.should == ["Expected -0.0", "not to be -0.0"]
+  end
+end