Assertions are validation rules applied to test results that check how your target web service performs during a test run.
Now, we will create an assertion that will check that the average simulation time of a single test step does not exceed some time limit:
Expand the test case and click the Response element of the test step you want to assert. The Request editor will be displayed.
In the Assertions section of the Request inspector, click :
In the subsequent Add Assertion dialog, select the Time Taken statistics and the Median metric using drop-down lists:
Configure other assertion parameters:
In the Maximum edit box, enter the maximum time the test step execution can take on average.
In the Tolerance section, set the maximum number of times the assertion should trigger before logging an error.
Click OK. LoadUI will add the assertion to your load test.
Run the test again. If the responses take too long, LoadUI will report errors. View the assertion errors in the Global Metrics graph and in the Test Step Metrics table: