add TypeFilter to additional filters

lib/mutations.rb

@@ -9,6 +9,7 @@
 require 'mutations/errors'
 require 'mutations/input_filter'
 require 'mutations/additional_filter'
+require 'mutations/type_filter'
 require 'mutations/string_filter'
 require 'mutations/integer_filter'
 require 'mutations/float_filter'

lib/mutations/type_filter.rb

@@ -0,0 +1,21 @@
+module Mutations
+  class TypeFilter < AdditionalFilter
+    @default_options = {
+      :nils => false,    # true allows an explicit nil to be valid. Overrides any other options
+      :klass => nil,     # require the input to be of this type
+    }
+
+    def filter(data)
+      if data.nil?
+        return [nil, nil] if options[:nils]
+        return [nil, :nils]
+      end
+
+      klass = options[:klass]
+      return [nil, :klass] unless klass.is_a?(Class)
+      return [nil, :invalid] unless data.is_a?(klass)
+
+      [data, nil]
+    end
+  end
+end

spec/type_filter_spec.rb

@@ -0,0 +1,64 @@
+require 'spec_helper'
+
+describe Mutations::TypeFilter do
+  let(:options){ {} }
+  let(:outcome){ Mutations::TypeFilter.new(options).filter(input) }
+  let(:result){ outcome[0] }
+  let(:errors){ outcome[1] }
+
+  describe 'klass input' do
+    class Foo
+    end
+
+    let(:options){ { klass: Foo } }
+
+    describe 'exactly klass' do
+      let(:input){ Foo.new }
+
+      it{ assert_equal(result, input) }
+      it{ assert_nil(errors) }
+    end
+
+    describe 'subclass of klass' do
+      let(:input){ Class.new(Foo).new }
+
+      it{ assert_equal(result, input) }
+      it{ assert_nil(errors) }
+    end
+
+    describe 'not a Class' do
+      let(:options){ { klass: 123 } }
+      let(:input){ Foo.new }
+
+      it{ assert_nil(result) }
+      it{ assert_equal(errors, :klass) }
+    end
+
+    describe 'not a klass' do
+      let(:input){ Class.new }
+
+      it{ assert_nil(result) }
+      it{ assert_equal(errors, :invalid) }
+    end
+
+  end
+
+  describe 'nil input' do
+    let(:input){ nil }
+
+    describe 'nils allowed' do
+      let(:options){ { nils: true } }
+
+      it{ assert_nil(result) }
+      it{ assert_nil(errors) }
+    end
+
+    describe 'nils not allowed' do
+      let(:options){ { nils: false } }
+
+      it{ assert_nil(result) }
+      it{ assert_equal(errors, :nils) }
+    end
+  end
+
+end