Use writeFileSync to write to out file

index.js

@@ -1,3 +1,4 @@
+const ConcatStream = require('concat-stream')
 const isRequire = require('is-require')()
 const through = require('through2')
 const falafel = require('falafel')
@@ -25,7 +26,7 @@ function cssExtract (bundle, opts) {
     bundle.pipeline.get('debug').unshift(through.obj(write, flush))
     const writeStream = (typeof outFile === 'function')
       ? outFile()
-      : fs.createWriteStream(outFile)
+      : ConcatStream(writeOutFile)
 
     function write (chunk, enc, cb) {
       const css = extract(chunk)
@@ -39,6 +40,10 @@ function cssExtract (bundle, opts) {
       cb()
     }
   }
+
+  function writeOutFile (buffer) {
+    fs.writeFileSync(outFile, buffer)
+  }
 }
 
 // extract css from chunks

package.json

@@ -20,6 +20,7 @@
   ],
   "license": "MIT",
   "dependencies": {
+    "concat-stream": "^1.5.1",
     "falafel": "^1.2.0",
     "is-require": "0.0.1",
     "through2": "^2.0.1"
@@ -32,7 +33,8 @@
     "istanbul": "^0.4.2",
     "sheetify": "^4.1.0",
     "standard": "^6.0.7",
-    "tape": "^4.5.0"
+    "tape": "^4.5.0",
+    "tmp": "0.0.28"
   },
   "files": [
     "index.js",

test/index.js

@@ -1,4 +1,5 @@
 const browserify = require('browserify')
+const tmpDir = require('tmp').dir
 const path = require('path')
 const test = require('tape')
 const bl = require('bl')
@@ -29,4 +30,28 @@ test('css-extract', function (t) {
       })
     }
   })
+
+  t.test('should write file', function (t) {
+    t.plan(3)
+    tmpDir({unsafeCleanup: true}, onDir)
+
+    function onDir (err, dir, cleanup) {
+      t.ifError(err, 'no error')
+      const outFile = path.join(dir, 'out.css')
+
+      browserify(path.join(__dirname, 'source.js'))
+        .transform('sheetify/transform')
+        .plugin(cssExtract, { out: outFile })
+        .bundle(function (err) {
+          t.ifError(err, 'no bundle error')
+
+          const exPath = path.join(__dirname, './expected.css')
+          const expected = fs.readFileSync(exPath, 'utf8').trim()
+          const actual = fs.readFileSync(outFile, 'utf8').trim()
+          t.equal(expected, actual, 'all css written to file')
+
+          cleanup()
+        })
+    }
+  })
 })