adds test

certificates/essentials/test.md

@@ -220,6 +220,7 @@
 	* D) `rn newfile.txt afile.txt`
 	* E) `touch newfile.txt afile.txt`
 2. You want to copy a directory, `MyFiles`, to a USB flash drive that uses the FAT filesystem. The contents of `MyFiles` are as follows:
+
 ```bash
 $ ls -l MyFiles/
 total 276
@@ -227,12 +228,14 @@ total 276
 -rw-r--r-- 1 rod  users  42667 Nov 8 15:12 outline.pdf
 -rw-r--r-- 1 sam  users 105979 Nov 8 15:12 Outline.PDF
 ```
+
 	The USB flash drive is mounted at `/media/usb`, and so you type `cp -a MyFiles /media/`. What problem will occur when you attempt to copy these files?
 	* A) The command will fail because it tries to create links.
 	* B) The `MyFiles` directory will be copied, but none of its files will be copied.
 	* C) One file will be missing on the USB flash drive.
 	* D) One file's name will be changed during the copy.
 	* E) Everything will be fine; the command will work correctly.
+
 3. You type `mkdir one/two/three` and receive an error message that reads, in part, `No such file or directory`. What can you do to overcome this problem? (Select all that apply.) 
 	* A) Add the `--parents` parameter to the `mkdir` command.
 	* B) Issue three separate `mkdir` commands: `mkdir one`, then `mkdir one/two`, and then `mkdir one/two/three`.