Updated based on recommended changes per review.

plugins/provisioners/ansible/cap/guest/pip/pip.rb

@@ -5,7 +5,7 @@ module VagrantPlugins
       module Guest
         module Pip
 
-          DEFAULT_PIP_INSTALL_CMD = "curl https://bootstrap.pypa.io/get-pip.py | sudo python"
+          DEFAULT_PIP_INSTALL_CMD = "curl https://bootstrap.pypa.io/get-pip.py | sudo python".freeze
 
           def self.pip_install(machine, package = "", version = "", pip_args = "", upgrade = true)
             upgrade_arg = "--upgrade" if upgrade
@@ -25,10 +25,10 @@ module VagrantPlugins
             # The objective here is to get pip either by default
             # or by the argument passed in. The objective is not 
             # to circumvent the pip setup by passing in nothing.
-            # Thus, we stick with the default on an empty string
-            # or if it is an UNSET_VALUE.
+            # Thus, we stick with the default on an empty string.
+            # Typecast added in the check for safety.
 
-            if pip_install_cmd == Vagrant.plugin("2", :config)::UNSET_VALUE || pip_install_cmd.empty?
+            if pip_install_cmd == pip_install_cmd.to_s.empty?
               pip_install_cmd=DEFAULT_PIP_INSTALL_CMD
             end
 

test/unit/plugins/provisioners/ansible/cap/guest/pip/pip_test.rb

@@ -24,29 +24,29 @@ describe VagrantPlugins::Ansible::Cap::Guest::Pip do
 
   describe "#get_pip" do
     describe 'when no pip_install_command argument is provided' do
-        it "installs pip using the default command" do
-            expect(communicator).to receive(:execute).with("curl https://bootstrap.pypa.io/get-pip.py | sudo python")
-            subject.get_pip(machine)
-        end
+      it "installs pip using the default command" do
+        expect(communicator).to receive(:execute).with("curl https://bootstrap.pypa.io/get-pip.py | sudo python")
+        subject.get_pip(machine)
+      end
     end
 
     describe 'when pip_install_command argument is provided' do
-        it "runs the supplied argument instead of default" do
-            pip_install_command = "foo"
-            expect(communicator).to receive(:execute).with(pip_install_command)
-            subject.get_pip(machine,pip_install_command)
-        end
+      it "runs the supplied argument instead of default" do
+        pip_install_command = "foo"
+        expect(communicator).to receive(:execute).with(pip_install_command)
+        subject.get_pip(machine,pip_install_command)
+      end
 
-        it "installs pip using the default command if the argument is empty" do
-            pip_install_command = ""
-            expect(communicator).to receive(:execute).with("curl https://bootstrap.pypa.io/get-pip.py | sudo python")
-            subject.get_pip(machine,pip_install_command)
-        end 
+      it "installs pip using the default command if the argument is empty" do
+        pip_install_command = ""
+        expect(communicator).to receive(:execute).with("curl https://bootstrap.pypa.io/get-pip.py | sudo python")
+        subject.get_pip(machine,pip_install_command)
+      end 
         
-        it "installs pip using the default command if the argument is UNSET_VALUE" do
-            expect(communicator).to receive(:execute).with("curl https://bootstrap.pypa.io/get-pip.py | sudo python")
-            subject.get_pip(machine, Vagrant.plugin("2", :config)::UNSET_VALUE)
-        end         
+      it "installs pip using the default command if the argument is nil" do
+        expect(communicator).to receive(:execute).with("curl https://bootstrap.pypa.io/get-pip.py | sudo python")
+        subject.get_pip(machine, nil)
+      end         
     end    
   end
 end