1 files changed, 49 insertions, 0 deletions
diff --git a/spec/rubyspec/core/float/prev_float_spec.rb b/spec/rubyspec/core/float/prev_float_spec.rb
new file mode 100644
index 0000000000..e07d78c44c
--- /dev/null
+++ b/spec/rubyspec/core/float/prev_float_spec.rb
@@ -0,0 +1,49 @@
+require File.expand_path('../../../spec_helper', __FILE__)
+
+describe "Float#prev_float" do
+  it "returns a float the smallest possible step smaller than the receiver" do
+    barely_negative = 0.0.prev_float
+    barely_negative.should == 0.0.prev_float
+
+    barely_negative.should < 0.0
+    barely_negative.should > barely_negative.prev_float
+
+    midpoint = barely_negative / 2
+    [0.0, barely_negative].should include midpoint
+  end
+
+  it "returns -Float::INFINITY for -Float::INFINITY" do
+    (-Float::INFINITY).prev_float.should == -Float::INFINITY
+  end
+
+  it "steps directly between MAX and INFINITY" do
+    Float::INFINITY.prev_float.should == Float::MAX
+    (-Float::MAX).prev_float.should == -Float::INFINITY
+  end
+
+  it "steps directly between 1.0 and 1.0 - EPSILON/2" do
+    1.0.prev_float.should == 1.0 - Float::EPSILON/2
+  end
+
+  it "steps directly between -1.0 and -1.0 - EPSILON" do
+    (-1.0).prev_float.should == -1.0 - Float::EPSILON
+  end
+
+  it "reverses the effect of next_float for all Floats except -INFINITY and -0.0" do
+    num = rand
+    num.next_float.prev_float.should == num
+  end
+
+  it "returns positive zero when stepping downward from just above zero" do
+    x = 0.0.next_float.prev_float
+    (1/x).should == Float::INFINITY
+  end
+
+  it "gives the same result for -0.0 as for +0.0" do
+    (0.0).prev_float.should == (-0.0).prev_float
+  end
+
+  it "returns NAN if NAN was the receiver" do
+    Float::NAN.prev_float.nan?.should == true
+  end
+end