   prefixed = "a { -webkit-transition: all 1s; transition: all 1s }"
 
   it 'shows autoprefixer version', (done) ->
-    @exec '-v', (out, err) ->
-      err.should.be.false
+    @run '-v', (out) ->
       out.should.match(/^autoprefixer [\d\.]+\n$/)
       done()
 
   it 'shows help instructions', (done) ->
-    @exec '-h', (out, err) ->
-      err.should.be.false
+    @run '-h', (out) ->
       out.should.match(/Usage:/)
       done()
 
   it 'shows selected browsers and properties', (done) ->
-    @exec '-i', (out, err) ->
-      err.should.be.false
+    @run '-i', (out) ->
       out.should.match(/Browsers:/)
       done()
 
   it 'changes browsers', (done) ->
-    @exec '-i', '-b', 'ie 6', (out, err) ->
-      err.should.be.false
+    @run '-i', '-b', 'ie 6', (out) ->
       out.should.match(/IE: 6/)
       done()
 
   it 'rewrites several files', (done) ->
     write('a.css', css)
     write('b.css', css + css)
-    @exec '-b', 'chrome 25', 'a.css', 'b.css', (out, err) ->
-      err.should.be.false
+    @run '-b', 'chrome 25', 'a.css', 'b.css', (out) ->
       out.should.eql ''
       read('a.css').should.eql prefixed
       read('b.css').should.eql prefixed + prefixed

          error = @stderr.content
        callback(@stdout.content, error)

  afterEach ->
    fs.removeSync(tempDir) if fs.existsSync(tempDir)



  it 'changes output file', (done) ->
    write('a.css', css)
    @run '-b', 'chrome 25', 'a.css', '-o', 'b.css', (out) ->
      out.should.eql ''
      read('a.css').should.eql css
      read('b.css').should.eql prefixed
