[Bug #21106] Fix tests for custom random object

When a positive integer limit is given, `rand` method of a RNG object
is expected to return a value between 0 and the limit (exclusive).

Fix shuffle_spec.rb like as the similar code in sample_spec.rb, and
add tests for greater values.

TODO:
- Return a value that is equal to or greater than the limit given to
  the RNG object.
- Extract common code about RNG objects to a shared file.

spec/ruby/core/array/sample_spec.rb

@@ -114,6 +114,13 @@ describe "Array#sample" do
 
         -> { [1, 2].sample(random: random) }.should raise_error(RangeError)
       end
+
+      it "raises a RangeError if the value is greater than the Array size" do
+        random = mock("array_sample_random")
+        random.should_receive(:rand).and_return(3)
+
+        -> { [1, 2].sample(random: random) }.should raise_error(RangeError)
+      end
     end
   end
 

spec/ruby/core/array/shuffle_spec.rb

@@ -69,9 +69,18 @@ describe "Array#shuffle" do
     -> { [1, 2].shuffle(random: random) }.should raise_error(RangeError)
   end
 
-  it "raises a RangeError if the value is equal to one" do
+  it "raises a RangeError if the value is equal to the Array size" do
     value = mock("array_shuffle_random_value")
-    value.should_receive(:to_int).at_least(1).times.and_return(1)
+    value.should_receive(:to_int).at_least(1).times.and_return(2)
+    random = mock("array_shuffle_random")
+    random.should_receive(:rand).at_least(1).times.and_return(value)
+
+    -> { [1, 2].shuffle(random: random) }.should raise_error(RangeError)
+  end
+
+  it "raises a RangeError if the value is greater than the Array size" do
+    value = mock("array_shuffle_random_value")
+    value.should_receive(:to_int).at_least(1).times.and_return(3)
     random = mock("array_shuffle_random")
     random.should_receive(:rand).at_least(1).times.and_return(value)