Added spec/examples/log_buffer_example_spec.rb

README.rdoc

@@ -113,6 +113,16 @@ for class method:
 
 Please see spec: http://github.com/kaorukobo/rhook/blob/master/spec/rhook_spec.rb
 
+== Practical Example
+
+=== 1. Log Buffer
+
+Log Buffer allows you to capture any messages written to Logger and keep in buffer.
+
+For example, you can examine the target program's log messages in testing code.
+
+http://github.com/kaorukobo/rhook/blob/master/spec/examples/log_buffer_example_spec.rb
+
 == ...
 
 === Note on Patches/Pull Requests

spec/examples/log_buffer_example_spec.rb

@@ -0,0 +1,66 @@
+require File.expand_path(File.dirname(__FILE__) + '/../spec_helper')
+
+describe "rhook examples" do
+  describe "log buffer (hack Logger)" do
+    require "logger"
+
+    # Captures any messages written to Logger and keep in buffer.
+    # You can read captured messages by LogBuffer#get 
+    # or LogBuffer##pull ( also clears buffer ). 
+    class LogBuffer
+      def initialize
+        @buf = ""
+        # Any log messages are passed to Logger#format_message. Hack it!!
+        Logger._rhook.hack(:format_message) do |inv|
+          result = inv.call
+          @buf << result
+          result
+        end
+      end
+
+      def clear
+        @buf = ""
+      end
+
+      def get
+        @buf
+      end
+
+      def pull
+        result = get()
+        clear()
+        result
+      end
+    end #/LogBuffer
+
+    # The example application to test.
+    # You cannot know whether it success or failed, (by return value or exception)
+    # ... it only logs.
+    class TargetApp
+      def initialize
+        @log = Logger.new(STDERR)
+      end
+
+      def success
+        @log.info "Success!"
+      end
+
+      def fail
+        @log.error "Failed!"
+      end
+    end
+
+    example "Use LogBuffer to write test" do
+      app = TargetApp.new
+
+      # start to capture log.
+      logbuf = LogBuffer.new
+
+      app.success
+      logbuf.pull.should match(/Success!/)
+
+      app.fail
+      logbuf.pull.should match(/Failed!/)
+    end
+  end
+end