bug fix and tests for std/node/fs/mkdir (#4917)

std/node/_fs/_fs_mkdir.ts

@@ -20,7 +20,7 @@ export function mkdir(
   let recursive = false;
 
   if (typeof options == "function") {
-    callback == options;
+    callback = options;
   } else if (typeof options === "number") {
     mode = options;
   } else if (typeof options === "boolean") {

std/node/_fs/_fs_mkdir_test.ts

@@ -0,0 +1,32 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+
+import { assert } from "../../testing/asserts.ts";
+import { mkdir, mkdirSync } from "./_fs_mkdir.ts";
+import { existsSync } from "./_fs_exists.ts";
+
+const { test } = Deno;
+
+const tmpDir = "./tmpdir";
+
+test({
+  name: "[node/fs] mkdir",
+  fn: async () => {
+    const result = await new Promise((resolve) => {
+      mkdir(tmpDir, (err) => {
+        err && resolve(false);
+        resolve(existsSync(tmpDir));
+        Deno.removeSync(tmpDir);
+      });
+    });
+    assert(result);
+  },
+});
+
+test({
+  name: "[node/fs] mkdirSync",
+  fn: () => {
+    mkdirSync(tmpDir);
+    assert(existsSync(tmpDir));
+    Deno.removeSync(tmpDir);
+  },
+});