#387 Added unit test for writing data using the Promise API

tests/spec/fs.write.spec.js

@@ -59,4 +59,28 @@ describe('fs.write', function() {
       });
     });
   });
+
+  it('should write data to a file using the Promise API', function(done) {
+    var fs = util.fs().promises;
+    var buffer = new Filer.Buffer([1, 2, 3, 4, 5, 6, 7, 8]);
+
+    fs.open('/myfile', 'w+')
+      .then((fd) => { 
+        fs.write(fd, buffer, 0, buffer.length, 0)
+          .then((result) => {
+            expect(result).to.equal(buffer.length);
+          });
+      })
+      .then(() => {
+        fs.stat('/myfile')
+          .then((result) => {
+            expect(result.type).to.equal('FILE');
+            expect(result.size).to.equal(buffer.length);
+          });
+      })
+      .catch(function(error) {
+        if(error) throw error;
+      })
+      .finally(done);
+  });
 });