Add shared_examples.rb file

Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>

spec/shared_examples.rb

@@ -0,0 +1,5 @@
+shared_examples_for "a Puppet::Error" do |description|
+  it "with message matching #{description.inspect}" do
+    expect { should have_class_count(1) }.to raise_error(Puppet::Error, description)
+  end
+end