Make BackgroundJobEnvironment specs work on linux

Also improve the test for the case without a readiness port. The
previous test only tested that a single specific port was not opened,
when any port may have been opened. The new test ensures that the same
number of ports are open before and after running the method. This may
cause problems when running tests in parallel, but we can address that
problem when/if it occurs

Authored-by: Matt Royal <mroyal@pivotal.io>

Author: matt-royal

spec/unit/lib/background_job_environment_spec.rb

@@ -39,17 +39,23 @@
       background_job_environment.setup_environment
     end
 
+    def open_port_count
+      `lsof -i -P -n | grep LISTEN | wc -l`.to_i
+    end
+
     it 'doesnt attempt to open a readiness port' do
-      expect { TCPSocket.new('localhost', 9999).close }.to raise_error(Errno::ECONNREFUSED)
-      background_job_environment.setup_environment
-      expect { TCPSocket.new('localhost', 9999).close }.to raise_error(Errno::ECONNREFUSED)
+      expect {
+        background_job_environment.setup_environment
+      }.not_to change { open_port_count }
     end
 
     context 'readiness_port provided' do
       it 'opens the readiness port' do
-        expect { TCPSocket.new('localhost', 9999).close }.to raise_error(Errno::ECONNREFUSED)
-        background_job_environment.setup_environment(9999)
-        expect { TCPSocket.new('localhost', 9999).close }.not_to raise_error
+        expect { TCPSocket.new('127.0.0.1', 9999).close }.to raise_error(Errno::ECONNREFUSED)
+        expect {
+          background_job_environment.setup_environment(9999)
+        }.to change { open_port_count }.by(1)
+        expect { TCPSocket.new('127.0.0.1', 9999).close }.not_to raise_error
       end
     end
   end