added tests for fs.promises.chown() closes #465 (#471)

* added tests for fs.promises.chown() for check if function exists and updating gid/uid for a file

* update to pass lint tests

* cleaned up code. replaced all callbacks with promises in new test.

* Revert "lint tests fix"

This reverts commit 3c256124cf, reversing
changes made to 71a6f514fc.

* Revert "cleaned up code. replaced all callbacks with promises in new test."

This reverts commit 71a6f514fc.

* Made requested changes.

tests/spec/fs.chown.spec.js

@@ -62,3 +62,27 @@ describe('fs.chown, fs.fchown', function() {
     });
   });
 });
+
+
+describe('fs.promises.chown', function(){
+  beforeEach(util.setup);
+  afterEach(util.setup);
+
+  it('should be a function', function(){
+    var fsPromises = util.fs().promises;
+    expect(fsPromises.chown).to.be.a('function');
+  });
+
+  it('should allow updating uid and gid for a file', function() {
+    var fsPromises = util.fs().promises;
+    return fsPromises.writeFile('/file', 'data')
+      .then(() => 
+        fsPromises.chown('/file', 500, 500))
+      .then(() => 
+        fsPromises.stat('/file'))
+      .then((stats) =>{
+        expect(stats.uid).to.equal(500);
+        expect(stats.gid).to.equal(500);
+      });
+  });
+});