Added tests for Promises version of mkdir (#415)

tests/spec/fs.mkdir.spec.js

@@ -45,13 +45,50 @@ describe('fs.mkdir', function() {
       });
     });
   });
+});
 
-  it('should return an error if the path already exists (using promises)', () => {
-    var fsPromises = util.fs().promises;
-    return fsPromises.mkdir('/').catch(error => {
+describe('fs.promises.mkdir', function () {
+  beforeEach(util.setup);
+  afterEach(util.cleanup);
+
+  it('should be a function', function () {
+    var fs = util.fs();
+    expect(fs.promises.mkdir).to.be.a('function');
+  });
+
+  it('should return an error if part of the parent path does not exist', function () {
+    var fs = util.fs();
+
+    return fs.promises.mkdir('/tmp/mydir')
+      .catch(error => {
+        expect(error).to.exist;
+        expect(error.code).to.equal('ENOENT');
+      });
+  });
+
+  it('should return an error if the path already exists', function () {
+    var fs = util.fs();
+
+    return fs.promises.mkdir('/')
+      .catch(error =>{
         expect(error).to.exist;
         expect(error.code).to.equal('EEXIST');
       });
   });
 
+  it('should make a new directory', function () {
+    var fs = util.fs();
+
+    return fs.promises.mkdir('/tmp')
+      .then(() => fs.promises.stat('/tmp'))
+      .then(stats => {
+        expect(stats).to.exist;
+        expect(stats.type).to.equal('DIRECTORY');
+      });
+  });
+
+  it('should return a promise', function () {
+    var fs = util.fs();
+    expect(fs.promises.mkdir('/tmp')).to.be.a('promise');
+  });
 });