Add Array#delete_if

mrbgems/mruby-array-ext/test/array.rb

@@ -223,3 +223,16 @@ assert("Array#insert") do
   b = ["a", "b", "c", "d"]
   assert_equal ["a", "b", "c", "d", nil, nil, 99], b.insert(6, 99)
 end
+
+assert("Array#delete_if") do
+  a = [1, 2, 3, 4, 5]
+  assert_equal [1, 2, 3, 4, 5], a.delete_if { false }
+  assert_equal [1, 2, 3, 4, 5], a
+
+  a = [1, 2, 3, 4, 5]
+  assert_equal [], a.delete_if { true }
+  assert_equal [], a
+
+  a = [ 1, 2, 3, 4, 5 ]
+  assert_equal [1, 2, 3], a.delete_if { |val| val > 3 }
+end