safeguard against empty backends

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>

bin/vulcano

@@ -73,6 +73,8 @@ class VulcanoCLI < Thor
     runner = Vulcano::Runner.new(options[:id], options)
     runner.add_tests(tests)
     runner.run
+  rescue RuntimeError => e
+    puts e.message
   end
 
 end

lib/vulcano/profile_context.rb

@@ -6,6 +6,11 @@ module Vulcano
 
     attr_reader :rules, :only_ifs
     def initialize profile_id, backend, profile_registry: {}, only_ifs: []
+      if backend.nil?
+        raise "ProfileContext is initiated with a backend == nil. " +
+              "This is a backend error which must be fixed upstream."
+      end
+
       @profile_id = profile_id
       @rules = profile_registry
       @only_ifs = only_ifs

lib/vulcano/runner.rb

@@ -25,27 +25,28 @@ module Vulcano
       @rules = []
       @profile_id = profile_id
       @conf = Vulcano::Backend.target_config(conf)
+      configure_output
+      configure_backend
+    end
 
+    def configure_output
       # RSpec.configuration.output_stream = $stdout
       # RSpec.configuration.error_stream = $stderr
       RSpec.configuration.add_formatter(:json)
+    end
 
+    def configure_backend
       # specinfra
       backend_name = @conf[:backend] || 'exec'
       backend_class = Vulcano::Backend.registry[backend_name]
       if backend_class.nil?
-        puts "Can't find command backend '#{backend_name}'."
-        return
+        raise "Can't find command backend '#{backend_name}'."
       end
 
       # create the backend based on the config
       @backend = backend_class.new(@conf.dup)
     end
 
-    def select_backend( conf )
-
-    end
-
     def add_tests(tests)
       items = tests.map do |test|
         Vulcano::Targets.resolve(test)