Here are some test which we can carried out to test Yahoo
messenger on single machine

1) Yahoo messenger installation.
2) Create Account Or Login
3) Add Friend/s 
3)Check whose are online to chat( Those are from  added)
4) Try to Chat 
5) file sending
6) Changing User status.

If I am wrong please correct me.

Thx
Sudhir Kulkarni

Dear sudhir,

the question is how would you cheak yahoo msg on single 
machine.... that is both the people who chat should use the 
same computer... and the problem is this that you can't 
open two yahoo msg on the same computer. So the question is 
how would you open two yahoo msengr.
neha

Dear Neha,

Yahoo messenger, by default, runs only a single copy on a
single machine so for people with multiple yahoo id's this
is a problem. Here is a short snippet that makes yahoo
messenger to run multiple versions.

REGEDIT
Open the registry editor.
Start > Run > regedit

Navigate to


+- HKEY_CURRENT_USER
   +- Software
      +- yahoo
          +- pager


Create a new key inside pager named Test
Now inside the Test folder create REG_DWORD named pluralwith
value 1.

Now you should be able to run multiple instances of yahoo
messenger.

by logging on to it

Simple way to do this is:

    * Go to START->RUN-> Type 'regedit' and press ENTER.
    * Then navigate to
'HKEY_CURRENT_USER\Software\Yahoo\Pager\Test'
    * Now in the right pane right click New->DWORD Value.
Name it as 'Plural'.
    * Now Double click the the Plural DWORD you created &
set the value to 1.

Now try login using two id's in a single machine.

How dumb! 
This question does not test anything. 
its like asking someone 
which is the nearest gas station. 

Pointless question

Install VMWare to test Yahoo messenger on single box.

just install vmware virtual machine & after that any 
automation testing tool like qtp, winrunner
record some functionality & playback for many users.