Add specs for Rational#truncate

spec/ruby/shared/rational/truncate.rb

@@ -1,5 +1,51 @@
 require File.expand_path('../../../spec_helper', __FILE__)
 
 describe :rational_truncate, :shared => true do
-  it "needs to be reviewed for spec completeness"
+  ruby_version_is ""..."1.9.2" do
+    it "needs to be reviewed for spec completeness"
+  end
+
+  ruby_version_is "1.9.2" do
+    before do
+      @rational = Rational(2200, 7)
+    end
+
+    describe "with no arguments (precision = 0)" do
+      it "returns an integer" do
+        @rational.truncate.should be_kind_of(Integer)
+      end
+
+      it "returns the truncated value toward 0" do
+        @rational.truncate.should == 314
+        Rational(1, 2).truncate.should == 0
+        Rational(-1, 2).truncate.should == 0
+      end
+    end
+
+    describe "with a precision < 0" do
+      it "returns an integer" do
+        @rational.truncate(-2).should be_kind_of(Integer)
+        @rational.truncate(-1).should be_kind_of(Integer)
+      end
+
+      it "moves the truncation point n decimal places left" do
+        @rational.truncate(-3).should == 0
+        @rational.truncate(-2).should == 300
+        @rational.truncate(-1).should == 310
+      end
+    end
+
+    describe "with a precision > 0" do
+      it "returns a Rational" do
+        @rational.truncate(1).should be_kind_of(Rational)
+        @rational.truncate(2).should be_kind_of(Rational)
+      end
+
+      it "moves the truncation point n decimal places right" do
+        @rational.truncate(1).should == Rational(1571, 5)
+        @rational.truncate(2).should == Rational(7857, 25)
+        @rational.truncate(3).should == Rational(62857, 200)
+      end
+    end
+  end
 end