Refactor #spawn_processes into #start(name)

When passed nil (aka ALL_PROCESSES) #start will start all processes in the
Procfile as per existing behavior

lib/foreman/engine.rb

@@ -15,6 +15,9 @@ class Foreman::Engine
   attr_reader :directory
   attr_reader :options
 
+  # This constant is here to make the invocations of #start and #stop methods
+  # clearer
+  ALL_PROCESSES = nil
   COLORS = %w( cyan yellow green magenta red blue intense_cyan intense_yellow
                intense_green intense_magenta intense_red, intense_blue )
 
@@ -36,12 +39,28 @@ class Foreman::Engine
     trap("INT")  { puts "SIGINT received";  terminate_gracefully }
 
     assign_colors
-    spawn_processes
+    start ALL_PROCESSES
     watch_for_output
     watch_for_termination
     terminate_gracefully
   end
 
+  def start(name)
+    concurrency = Foreman::Utils.parse_concurrency(@options[:concurrency])
+
+    procfile.entries.each do |entry|
+      unless name == ALL_PROCESSES
+        next unless entry.name == name
+      end
+
+      reader, writer = (IO.method(:pipe).arity == 0 ? IO.pipe : IO.pipe("BINARY"))
+      entry.spawn(concurrency[entry.name], writer, @directory, @environment, port_for(entry, 1, base_port)).each do |process|
+        running_processes[process.pid] = process
+        readers[process] = reader
+      end
+    end
+  end
+
   def stop(name, signal='SIGTERM')
     running_processes.each do |pid, process|
       unless name.nil?
@@ -77,18 +96,6 @@ class Foreman::Engine
 
 private ######################################################################
 
-  def spawn_processes
-    concurrency = Foreman::Utils.parse_concurrency(@options[:concurrency])
-
-    procfile.entries.each do |entry|
-      reader, writer = (IO.method(:pipe).arity == 0 ? IO.pipe : IO.pipe("BINARY"))
-      entry.spawn(concurrency[entry.name], writer, @directory, @environment, port_for(entry, 1, base_port)).each do |process|
-        running_processes[process.pid] = process
-        readers[process] = reader
-      end
-    end
-  end
-
   def base_port
     options[:port] || 5000
   end

spec/foreman/engine_spec.rb

@@ -57,7 +57,7 @@ describe "Foreman::Engine", :fakefs do
       stub(Process).fork
       any_instance_of(Foreman::Engine) do |engine|
         stub(engine).info
-        stub(engine).spawn_processes
+        stub(engine).start
         stub(engine).watch_for_termination
       end
     end