You can use my mgrep function, downloadable form the file exchange.
In your case, if you want to search for use of that file in your code,
mgrep test.mat . recurse off
The above command will cause mgrep to search for the string 'test.mat'. EVERY file in the current directory will be searched. The directory it will look in is the "dot" directory, that is, the current directory. If you wanted to specify some other directory, then just specify the complete directory path instead of the . in that command.
Finally, the nature of mgrep is by default to then search iteratively down all subdirectories below the one shosen. If you want it to search ONLY the current directory, you would do as I did, set recurse to off.
The default behavior of mgrep is to also show the line where that string occurs. You can turn that off. You can also set a case preference.
For example, I just used this tool, to search in the complete directory of files I've ever written, searching for occurences of the string 'usage'. Here are a few of the hundreds of cases where it found that string.
>> mgrep usage . recurse off
As you can see, it shows which file the call occurs in, as well as the line where it found that string.
You can download mgrep here: