Add `Array#sample` test

And simplify tests for `Array#shuffle` and `Array#shuffle!`.

mrbgems/mruby-random/test/random.rb

@@ -39,28 +39,20 @@ assert("return class of Kernel.rand") do
 end
 
 assert("Array#shuffle") do
-  ary = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
-  orig = ary.dup
+  orig = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+  ary = orig.dup
   shuffled = ary.shuffle
   assert_equal(orig, ary)
   assert_not_equal(ary, shuffled)
-  assert_equal(ary.size, shuffled.size)
-  shuffled.each do |x|
-    assert_include(ary, x)
-    ary.delete(x)
-  end
+  assert_equal(orig, shuffled.sort)
 end
 
 assert('Array#shuffle!') do
-  ary = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
-  orig = ary.dup
+  orig = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+  ary = orig.dup
   assert_same(ary, ary.shuffle!)
   assert_not_equal(orig, ary)
-  assert_equal(orig.size, ary.size)
-  ary.each do |x|
-    assert_include(orig, x)
-    orig.delete(x)
-  end
+  assert_equal(orig, ary.sort)
 end
 
 assert("Array#shuffle(random)") do
@@ -94,3 +86,37 @@ assert('Array#shuffle!(random)') do
   assert_equal(ary1, ary2)
   assert_not_equal(ary1, ary3)
 end
+
+assert('Array#sample') do
+  100.times do
+    assert_include([0, 1, 2], [2, 1, 0].sample)
+    [2, 1, 0].sample(2).each { |sample| assert_include([0, 1, 2], sample) }
+    h = {}
+    (1..10).to_a.sample(7).each do |sample|
+      assert_not_include(h, sample)
+      h[sample] = true
+    end
+  end
+
+  assert_nil([].sample)
+  assert_equal([], [].sample(1))
+  assert_equal([], [2, 1].sample(0))
+  assert_raise(TypeError) { [2, 1].sample(true) }
+  assert_raise(ArgumentError) { [2, 1].sample(-1) }
+end
+
+assert('Array#sample(random)') do
+  assert_raise(TypeError) do
+    # this will cause an exception due to the wrong argument
+    [1, 2].sample(2, "Not a Random instance")
+  end
+
+  # verify that the same seed causes the same results
+  ary = (1..10).to_a
+  srand(15)
+  samples1 = ary.sample(4)
+  samples2 = ary.sample(4, Random.new(15))
+  samples3 = ary.sample(4, Random.new(16))
+  assert_equal(samples1, samples2)
+  assert_not_equal(samples1, samples3)
+end