 <p>As far as I can tell from my experiments each top-level test, ie each test named in the load test, gets its own copy of the data sources of called tests. Hence even though the data source is attached to the called (ie login) test each calling test will use all of its values.</p> <p><strong>My experiment:</strong> A very simple web test named <code>Called</code> has a CSV data source having 100 rows and a column containing the row number. This web test just visits <code>http://localhost/</code> and expects a 404 response. A <code>WebTestPlugin</code> has a <code>PostWebTest</code> method that writes the data source's row number field plus the context parameters <code>$WebTestIteration</code> and <code>WebTestUserId</code> to a log file. A second test has as its only actions (1) a call of <code>Called</code> and (2) a call of the plugin. Made copies of this second test and gave them the names <code>Caller1</code>, <code>Caller2</code> and <code>Caller3</code>. These three tests are used in a load test for 6 virtual users for 2 minutes duration. The log file clearly shows that each CSV row is used by each of the three top-level tests.</p>