Started implementing cassette cache.

lib/vcr/cassette/cache.rb

@@ -1,18 +1,28 @@
 module VCR
   class Cassette
     class Cache
+      def initialize
+        @files = Hash.new do |files, file_name|
+          files[file_name] = File.exist?(file_name) ?
+                             File.read(file_name) :
+                             nil
+        end
+      end
+
       def [](file_name)
-        File.read(file_name)
+        @files[file_name]
+      end
+
+      def exists_with_content?(file_name)
+        @files[file_name].to_s.size > 0
       end
 
+      # TODO: test me
       def []=(file_name, content)
         directory = File.dirname(file_name)
         FileUtils.mkdir_p directory unless File.exist?(directory)
         File.open(file_name, 'w') { |f| f.write content }
-      end
-
-      def exists_with_content?(file_name)
-        File.size?(file_name)
+        @files[file_name] = content
       end
     end
   end

spec/vcr/cassette/cache_spec.rb

@@ -0,0 +1,69 @@
+require 'vcr/cassette/cache'
+
+module VCR
+  class Cassette
+    describe Cache do
+      describe "#[]" do
+        let(:content)   { "the file content" }
+        let(:file_name) { "file.yml" }
+
+        it 'only reads the file once' do
+          File.stub(:exist?).with(file_name).and_return(true)
+          File.should_receive(:read).with(file_name).once.and_return(content)
+          subject[file_name].should eq(content)
+          subject[file_name].should eq(content)
+          subject[file_name].should eq(content)
+        end
+      end
+
+      describe "#exists_with_content?" do
+        context 'when the file exists with no content' do
+          let(:file_name) { "zero_bytes.yml" }
+
+          before(:each) do
+            File.stub(:exist?).with(file_name).and_return(true)
+            File.stub(:read).with(file_name).and_return("")
+          end
+
+          it 'returns false' do
+            subject.exists_with_content?(file_name).should be_false
+          end
+
+          it 'does not read the file multiple times' do
+            File.should_receive(:read).once
+            subject.exists_with_content?(file_name)
+            subject.exists_with_content?(file_name)
+            subject.exists_with_content?(file_name)
+          end
+
+          it "does not check for the file's existence multiple times" do
+            File.should_receive(:exist?).once
+            subject.exists_with_content?(file_name)
+            subject.exists_with_content?(file_name)
+            subject.exists_with_content?(file_name)
+          end
+        end
+
+        context 'when the file does not exist' do
+          let(:file_name) { "non_existant_file.yml" }
+
+          it 'returns false' do
+            subject.exists_with_content?(file_name).should be_false
+          end
+
+          it 'does not attempt to read the file' do
+            File.should_not_receive(:read)
+            subject.exists_with_content?(file_name)
+          end
+
+          it "does not check for the file's existence multiple times" do
+            File.should_receive(:exist?).once.with(file_name).and_return(false)
+            subject.exists_with_content?(file_name)
+            subject.exists_with_content?(file_name)
+            subject.exists_with_content?(file_name)
+          end
+        end
+      end
+    end
+  end
+end