     beforeEach (done) ->
       promises = [
         q.nfcall(
-          fs.readFile,
+          fs.readFile.bind fs.readFile,
           "./tests/data/imports/main.css"
         ).then(
           (data) -> right.content = removeMapFile(

        ->
          promises = []
          promises.push q.nfcall(
            fs.readFile,
            "./tests/results/imports/main.css"
          ).then(
            (data) -> expect(

      promises = []
      targetFiles.forEach (file) ->
        promises.push q.nfcall(
          fs.readFile.bind fs.readFile,
          path.join("./tests/data/multiple", file)
        ).then(
          (data) ->
