For async mkdir, call the callback when passed as the third argument

This is for parity with the Node.js fs.mkdir implementation, which
may accept optional options as the 2nd argument.

Author: Spencer Elliott

lib/MemoryFileSystem.js

@@ -273,7 +273,7 @@ MemoryFileSystem.prototype.createWriteStream = function(path, options) {
 
 // async functions
 
-["stat", "readdir", "mkdirp", "mkdir", "rmdir", "unlink", "readlink"].forEach(function(fn) {
+["stat", "readdir", "mkdirp", "rmdir", "unlink", "readlink"].forEach(function(fn) {
 	MemoryFileSystem.prototype[fn] = function(path, callback) {
 		try {
 			var result = this[fn + "Sync"](path);
@@ -284,23 +284,25 @@ MemoryFileSystem.prototype.createWriteStream = function(path, options) {
 	};
 });
 
+["mkdir", "readFile"].forEach(function(fn) {
+	MemoryFileSystem.prototype[fn] = function(path, optArg, callback) {
+		if(!callback) {
+			callback = optArg;
+			optArg = undefined;
+		}
+		try {
+			var result = this[fn + "Sync"](path, optArg);
+		} catch(e) {
+			return callback(e);
+		}
+		return callback(null, result);
+	};
+});
+
 MemoryFileSystem.prototype.exists = function(path, callback) {
 	return callback(this.existsSync(path));
 }
 
-MemoryFileSystem.prototype.readFile = function(path, optArg, callback) {
-	if(!callback) {
-		callback = optArg;
-		optArg = undefined;
-	}
-	try {
-		var result = this.readFileSync(path, optArg);
-	} catch(e) {
-		return callback(e);
-	}
-	return callback(null, result);
-};
-
 MemoryFileSystem.prototype.writeFile = function (path, content, encoding, callback) {
 	if(!callback) {
 		callback = encoding;

test/MemoryFileSystem.js

@@ -65,6 +65,13 @@ describe("directory", function() {
 		stat.isDirectory().should.be.eql(true);
 		fs.readdirSync("D:\\//a/depth/\\sub").should.be.eql(["dir"]);
 	});
+	it("should call a mkdir callback when passed as the third argument", function(done) {
+		var fs = new MemoryFileSystem();
+		fs.mkdir('/test', {}, function(err) {
+			if (err) throw err;
+			done();
+		});
+	});
 });
 describe("files", function() {
 	it("should make and remove files", function() {