Travis tests for Windows and fix for failing test

.travis.yml

@@ -3,3 +3,7 @@ node_js:
   - '6'
   - '8'
   - node
+os:
+  - windows
+  - osx
+  - linux

index.js

@@ -144,13 +144,25 @@ function open (self, mode, req) {
 
   function onopen (err, fd) {
     if (err) return req.callback(err)
-
     var old = self.fd
     self.fd = fd
-    if (!old) return oncloseoldfd(null)
 
-    // if we are moving from readonly -> readwrite, close the old fd
-    fs.close(old, oncloseoldfd)
+    // fs.open on Linux fails with an error on a directory, but on Windows it
+    // returns a file descriptor to the dir, which we don't want.
+    // https://nodejs.org/api/fs.html#fs_file_system_flags
+    fs.fstat(fd, function (err, stats) {
+      if (err) return onerrorafteropen(err)
+      if (stats.isDirectory()) {
+        var error = new Error('EISDIR: illegal operation on a directory, open \'' + self.filename + '\'')
+        error.code = 'EISDIR'
+        return onerrorafteropen(error)
+      }
+
+      if (!old) return oncloseoldfd(null)
+
+      // if we are moving from readonly -> readwrite, close the old fd
+      fs.close(old, oncloseoldfd)
+    })
   }
 
   function oncloseoldfd (err) {

test.js

@@ -170,6 +170,28 @@ tape('write/read big chunks', function (t) {
   }
 })
 
+tape('destroy', function (t) {
+  var name = gen()
+  var file = raf(name)
+
+  file.write(0, Buffer.from('hi'), function (err) {
+    t.error(err, 'no error')
+    file.read(0, 2, function (err, buf) {
+      t.error(err, 'no error')
+      t.same(buf, Buffer.from('hi'))
+      file.destroy(ondestroy)
+    })
+  })
+
+  function ondestroy (err) {
+    t.error(err, 'no error')
+    fs.stat(name, function (err) {
+      t.same(err && err.code, 'ENOENT', 'should be removed')
+      t.end()
+    })
+  }
+})
+
 tape('rmdir option', function (t) {
   var name = path.join('rmdir', ++i + '', 'folder', 'test.txt')
   var file = raf(name, {rmdir: true, directory: tmp})