Open Visual Studio 2010 and create a new Test Project and
then record a new Web Performance Test.

When the browser opens as part of the recorder, go to your
favorite search engine, and search for something. Then stop the recording and
wait while Visual Studio detects dynamic parameters. Depending on the search
engine you're using, you may end up with a fair number of requests (due to
various images as well as AJAX script callbacks) in your recording. Find the
one that corresponds to your actual search request and delete the others.
For our test data, we're going to use a simple text file.
Go to your test project and add a new file. Name it SearchTerms.csv. Add
three rows of text to the file and save it:
Term
one
two
three
Next, in the QueryString Parameters of your search request,
click on the term you searched for and then inspect its properties.

From the dropdown beside the Value's value, choose Add Data
Source.

The simplest way to add data to your test is to create a
comma-separated file and include it in the test project. We'll use this
approach for now, but certainly you could also store the test data in an actual
database. Name the data source 'search terms', and click Next.

Next, select your SearchTerms.csv file from your test
project. You should see it added to your Web Test like so:

Now go back to your query parameter (in my case, q=aspalliance)
and inspect its properties. When you look at that value, you should have the
option to replace it with an item from the data source.

Choose the Term from the CSV file. Finally, delete all of
the other QueryString parameters except for your term, so it should look like
this:

Now you're ready to run the test. You should see results
like this:

Notice that we searched for our first search term, 'one'.
But wait, we only did one search - I thought the whole data file thing was
meant to let us run many different cases? So it is. The last step is to click
on the Edit run settings link above. Click the One run per data source row
option:

Now run the test again - you should get three test runs.
You can inspect each one to see the parameters that were passed in, as you can
see the 'three' shown here:

You can edit your test run settings in your .testsettings
file, which you'll find in your Solution items by default (e.g.
Local.testsettings). Under Web Test you'll find the setting to run the web
tests once per data row: