allow to give a specific revision to builder#build

lib/integrity/builder.rb

@@ -11,8 +11,12 @@ def initialize(project)
       @build = Build.new(:project => project)
     end
 
-    def build
-      @scm.with_latest_code { run_build_script }
+    def build(commit=nil)
+      if commit
+        @scm.with_revision(commit) { run_build_script }
+      else
+        @scm.with_latest_code { run_build_script }
+      end
       @build
     ensure
       @build.commit = @scm.head

spec/builder_spec.rb

@@ -67,6 +67,14 @@ def mock_scm(messages={})
       end
       @builder.build
     end
+
+    it 'should checkout the given commit from the scm and run the build script' do
+      mock_scm.should_receive(:with_revision).
+        with('6437fa27779daba40dbd130e2937d36253be1d4c').and_yield do
+          @builder.should_receive(:run_build_script)
+        end
+      @builder.build('6437fa27779daba40dbd130e2937d36253be1d4c')
+    end
 
     it "should assign the head of the SCM as the commit in the build" do
       mock_build.should_receive(:commit=).with mock_scm.head