1 files changed, 62 insertions, 0 deletions
diff --git a/spec/ruby/library/bigdecimal/sub_spec.rb b/spec/ruby/library/bigdecimal/sub_spec.rb
new file mode 100644
index 0000000000..3b62a0c794
--- /dev/null
+++ b/spec/ruby/library/bigdecimal/sub_spec.rb
@@ -0,0 +1,62 @@
+require_relative '../../spec_helper'
+require 'bigdecimal'
+
+describe "BigDecimal#sub" do
+
+  before :each do
+    @one = BigDecimal("1")
+    @zero = BigDecimal("0")
+    @two = BigDecimal("2")
+    @three = BigDecimal("3")
+    @nan = BigDecimal("NaN")
+    @infinity = BigDecimal("Infinity")
+    @infinity_minus = BigDecimal("-Infinity")
+    @one_minus = BigDecimal("-1")
+    @frac_1 = BigDecimal("1E-99999")
+    @frac_2 = BigDecimal("0.9E-99999")
+    @frac_3 = BigDecimal("12345E10")
+    @frac_4 = BigDecimal("98765E10")
+  end
+
+  it "returns a - b with given precision" do
+    # documentation states, that precision is optional
+    # but implementation raises ArgumentError if not given.
+
+    @two.sub(@one, 1).should == @one
+    @one.sub(@two, 1).should == @one_minus
+    @one.sub(@one_minus, 1).should == @two
+    @frac_2.sub(@frac_1, 1000000).should == BigDecimal("-0.1E-99999")
+    @frac_2.sub(@frac_1, 1).should == BigDecimal("-0.1E-99999")
+    # the above two examples puzzle me.
+    in_arow_one = BigDecimal("1.23456789")
+    in_arow_two = BigDecimal("1.2345678")
+    in_arow_one.sub(in_arow_two, 10).should == BigDecimal("0.9E-7")
+    @two.sub(@two,1).should == @zero
+    @frac_1.sub(@frac_1, 1000000).should == @zero
+  end
+
+  describe "with Rational" do
+    it "produces a BigDecimal" do
+      (@three - Rational(500, 2)).should == BigDecimal('-0.247e3')
+    end
+  end
+
+  it "returns NaN if NaN is involved" do
+    @one.sub(@nan, 1).should.nan?
+    @nan.sub(@one, 1).should.nan?
+  end
+
+  it "returns NaN if both values are infinite with the same signs" do
+    @infinity.sub(@infinity, 1).should.nan?
+    @infinity_minus.sub(@infinity_minus, 1).should.nan?
+  end
+
+  it "returns Infinity or -Infinity if these are involved" do
+    @infinity.sub(@infinity_minus, 1).should == @infinity
+    @infinity_minus.sub(@infinity, 1).should == @infinity_minus
+    @zero.sub(@infinity, 1).should == @infinity_minus
+    @frac_2.sub( @infinity, 1).should == @infinity_minus
+    @two.sub(@infinity, 1).should == @infinity_minus
+  end
+
+end