Define and apply matcher :be_rendered

Add this changes to make components specs clear

spec/support/matchers/be_rendered.rb

@@ -0,0 +1,13 @@
+RSpec::Matchers.define :be_rendered do
+  match do |page|
+    !page.native.inner_html.empty?
+  end
+
+  failure_message_when_negated do |page|
+    if page.has_css?("body")
+      "expected page not to be rendered, but was rendered with #{page.find("body").native.inner_html}"
+    else
+      "expected page not to be rendered, but was rendered with #{page.native.inner_html}"
+    end
+  end
+end