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

    before (done) ->
      targetPromises = [
        q.nfcall(
          fs.readFile,
          "./tests/data/single/source.css"
        ).then(
          (css) -> right.file = removeMapFile(css.toString "utf-8").trim()
        )
        q.nfcall(
          fs.readFile,
          "./tests/data/single/source.css.map"
        ).then(
          (map) ->
            right.sourcemap = JSON.parse(map.toString "utf-8")
            right.sourcemap.sources = right.sourcemap.sources.map(
              (file) -> path.relative(
                process.cwd(), path.resolve "./tests/data/single", file

                ).equal right[resultPath].content
            )
            promises.push q.nfcall(
              fs.readFile.bind fs.readFile,
              resultPath + ".map"
            ).then(
              (map) ->
