Switch between fake & real fs.

lib/memfs.rb

@@ -70,7 +70,7 @@ def activate
   #
   # @see #deactivate!
   # @return nothing.
-  def activate!
+  def activate!(clear: true)
     Object.class_eval do
       remove_const :Dir
       remove_const :File
@@ -79,7 +79,7 @@ def activate!
       const_set :File, MemFs::File
     end
 
-    MemFs::FileSystem.instance.clear!
+    MemFs::FileSystem.instance.clear! if clear
   end
   module_function :activate!
 
@@ -100,6 +100,26 @@ def deactivate!
   end
   module_function :deactivate!
 
+  # Switches back to the original file system, calls the given block (if any),
+  # and switches back afterwards.
+  # 
+  # If a block is given, all file & dir operations (like reading dir contents or
+  # requiring files) will operate on the original fs. 
+  # 
+  # @example
+  #   MemFs.halt do
+  #     puts Dir.getwd
+  #   end
+  # @return nothing
+  def halt
+    deactivate!
+
+    yield if block_given?
+  ensure
+    activate!(clear: false) 
+  end
+  module_function :halt
+
   # Creates a file and all its parent directories.
   #
   # @param path: The path of the file to create.

spec/memfs_spec.rb

@@ -50,6 +50,36 @@
     end
   end
 
+  describe '.halt' do
+    before :each do
+      described_class.activate!
+      described_class.deactivate!
+    end
+
+    it 'switches back to the original Ruby Dir & File classes' do
+      described_class.halt do
+        expect(::Dir).to be(described_class::OriginalDir)
+        expect(::File).to be(described_class::OriginalFile)
+      end
+    end
+
+    it 'switches back to the faked Dir & File classes' do
+      described_class.halt
+      expect(::Dir).to be(described_class::Dir)
+      expect(::File).to be(described_class::File)
+    end
+
+    it 'maintains the state of the faked fs' do
+      _fs.touch('file.rb')
+
+      described_class.halt do
+        expect(File.exist?('file.rb')).to be false
+      end
+
+      expect(File.exist?('file.rb')).to be true
+    end
+  end
+
   describe '.touch' do
     around(:each) { |example| described_class.activate { example.run } }