Add implementation for matching view elements in QA

qa/qa/page/base.rb

@@ -48,6 +48,10 @@ module QA
         @evaluator ||= Page::Base::DSL.new
       end
 
+      def self.validator
+        Page::Validator.new(self)
+      end
+
       class DSL
         attr_reader :views
 

qa/qa/page/element.rb

@@ -7,6 +7,18 @@ module QA
         @name = name
         @pattern = pattern
       end
+
+      def expression?
+        @pattern.is_a?(Regexp)
+      end
+
+      def matches?(line)
+        if expression?
+          line =~ pattern
+        else
+          line.includes?(pattern)
+        end
+      end
     end
   end
 end

qa/qa/page/validator.rb

@@ -0,0 +1,18 @@
+module QA
+  module Page
+    class Validator
+      def initialize(page)
+        @page = page
+        @views = page.views
+      end
+
+      def errors
+        @errors ||= @views.map do |view|
+        end
+      end
+
+      def message
+      end
+    end
+  end
+end

qa/qa/page/view.rb

@@ -8,6 +8,27 @@ module QA
         @elements = elements
       end
 
+      def pathname
+        Pathname.new(File.join( __dir__, '../../../', @path))
+          .cleanpath.expand_path
+      end
+
+      def errors
+        ##
+        # Reduce required elements by streaming views and making assertions on
+        # elements' patterns.
+        #
+        @missing ||= @elements.dup.tap do |elements|
+          File.new(pathname.to_s).foreach do |line|
+            elements.reject! { |element| element.matches?(line) }
+          end
+        end
+
+        @missing.map do |missing|
+          "Missing element `#{missing}` in `#{pathname}` view partial!"
+        end
+      end
+
       def self.evaluate(&block)
         Page::View::DSL.new.tap do |evaluator|
           evaluator.instance_exec(&block)

qa/spec/page/view_spec.rb

@@ -0,0 +1,61 @@
+describe QA::Page::View do
+  let(:element) do
+    double('element', name: :something, pattern: /some element/)
+  end
+
+  subject { described_class.new('some/file.html', [element]) }
+
+  describe '.evaluate' do
+    it 'evaluates a block and returns a DSL object' do
+      results = described_class.evaluate do
+        element :something, 'my pattern'
+        element :something_else, /another pattern/
+      end
+
+      expect(results.elements.size).to eq 2
+    end
+  end
+
+  describe '#pathname' do
+    it 'returns an absolute and clean path to the view' do
+      expect(subject.pathname.to_s).not_to include 'qa/page/'
+      expect(subject.pathname.to_s).to include 'some/file.html'
+    end
+  end
+
+  describe '#errors' do
+    let(:file) { spy('file') }
+
+    before do
+      allow(File).to receive(:new).and_return(file)
+    end
+
+    context 'when pattern is found' do
+      before do
+        allow(file).to receive(:foreach)
+          .and_yield('some element').once
+        allow(element).to receive(:matches?)
+          .with('some element').and_return(true)
+      end
+
+      it 'walks through the view and asserts on elements existence' do
+        expect(subject.errors).to be_empty
+      end
+    end
+
+    context 'when pattern has not been found' do
+      before do
+        allow(file).to receive(:foreach)
+          .and_yield('some element').once
+        allow(element).to receive(:matches?)
+          .with('some element').and_return(false)
+      end
+
+      it 'returns an array of errors related to missing elements' do
+        expect(subject.errors).not_to be_empty
+        expect(subject.errors.first)
+          .to match %r(Missing element `.*` in `.*/some/file.html` view)
+      end
+    end
+  end
+end