Add support for running Rake task in a clean environment

Changelog.md

@@ -15,6 +15,8 @@ Enhancements:
   (Viktor Fonic, #2634)
 * Issue warning when invalid values are used for `RSpec::Configuration#fail_fast`
   (Viktor Fonic, #2634)
+* Add support for running the Rake task in a clean environment.
+  (Jon Rowe, #2632)
 
 Bug Fixes:
 

lib/rspec/core/rake_task.rb

@@ -45,6 +45,21 @@ class RakeTask < ::Rake::TaskLib
       # A message to print to stderr when there are failures.
       attr_accessor :failure_message
 
+      if RUBY_VERSION < "1.9.0" || Support::Ruby.jruby?
+        # Run RSpec with a clean (empty) environment is not supported
+        def with_clean_environment=(_value)
+          raise ArgumentError, "Running in a clean environment is not supported on Ruby versions before 1.9.0"
+        end
+
+        # Run RSpec with a clean (empty) environment is not supported
+        def with_clean_environment
+          false
+        end
+      else
+        # Run RSpec with a clean (empty) environment.
+        attr_accessor :with_clean_environment
+      end
+
       # Use verbose output. If this is set to true, the task will print the
       # executed spec command to stdout. Defaults to `true`.
       attr_accessor :verbose
@@ -76,7 +91,12 @@ def run_task(verbose)
         command = spec_command
         puts command if verbose
 
-        return if system(command)
+        if with_clean_environment
+          return if system({}, command, :unsetenv_others => true)
+        else
+          return if system(command)
+        end
+
         puts failure_message if failure_message
 
         return unless fail_on_error

spec/rspec/core/rake_task_spec.rb

@@ -148,6 +148,24 @@ def silence_output(&block)
       end
     end
 
+    context "with_clean_environment is set" do
+      it "removes the environment variables", :if => RUBY_VERSION >= '1.9.0', :unless => RSpec::Support::Ruby.jruby? do
+        with_env_vars 'MY_ENV' => 'ABC' do
+          if RSpec::Support::OS.windows?
+            essential_shell_variables = /\["ANSICON", "ANSICON_DEF", "HOME", "TMPDIR", "USER"\]/
+          else
+            essential_shell_variables = /\["PWD"(?:, "SHLVL")?(?:, "_")?(?:, "__CF_USER_TEXT_ENCODING")?\]/
+          end
+
+          expect {
+            task.with_clean_environment = true
+            task.ruby_opts = '-e "puts \"Environment: #{ENV.keys}\""'
+            task.run_task false
+          }.to avoid_outputting.to_stderr.and output(essential_shell_variables).to_stdout_from_any_process
+        end
+      end
+    end
+
     def loaded_files
       args = Shellwords.split(spec_command)
       args -= [task.class::RUBY, "-S", task.rspec_path]