Add validator for integer arrays

Example usage:

    validates :related_post_ids, integer_array: true

spec/validators/integer_array_validator_spec.rb

@@ -0,0 +1,57 @@
+require "spec_helper"
+
+describe IntegerArrayValidator do
+  class TestModel
+    include ActiveModel::Validations
+
+    attr_accessor :ids
+
+    validates :ids, integer_array: true
+  end
+
+  describe "internationalization" do
+    it "has translation for NOT_ARRAY_ERROR" do
+      expect(described_class::NOT_ARRAY_ERROR).not_to be_blank
+    end
+
+    it "has translation for INVALID_ELEMENT_ERROR" do
+      expect(described_class::INVALID_ELEMENT_ERROR).not_to be_blank
+    end
+  end
+
+  describe "validation" do
+    let(:instance) { TestModel.new }
+
+    it "does not add error when nil" do
+      instance.ids = nil
+      expect(instance).to be_valid
+    end
+
+    it "does not add error when blank array" do
+      instance.ids = []
+      expect(instance).to be_valid
+    end
+
+    it "adds error NOT_ARRAY_ERROR when neither nil nor an array" do
+      instance.ids = 1
+      expect(instance).not_to be_valid
+      expect(instance.errors[:ids]).to include(described_class::NOT_ARRAY_ERROR)
+    end
+
+    it "does not add error when array of integers" do
+      instance.ids = [1, 2, 3]
+      expect(instance).to be_valid
+    end
+
+    it "does not add error when array of integers as String" do
+      instance.ids = ["1", "2", "3"]
+      expect(instance).to be_valid
+    end
+
+    it "adds error INVALID_ELEMENT_ERROR when an element cannot be parsed as Integer" do
+      instance.ids = [1, "2", "Not Integer", 3]
+      expect(instance).not_to be_valid
+      expect(instance.errors[:ids]).to include(described_class::INVALID_ELEMENT_ERROR)
+    end
+  end
+end