How to append test result to an old existing file? I want test results to be saved in a single file.

You can follow this tutorial append JMeter test result to an old existing file.

1. Start JMeter on your computer and open "\fyicenter\First-Load-Test-2.jmx".

2. Run the test plan again. You will get a warning message:

The file Test-Result.csv already exist, what do you want to do? 
Note you can avoid this popup by defining property 
'resultcollector.action_if_file_exists'.

[Append to existing file] [Don't start] [Overwrite existing file]

3. Select "Append to existing file" to finish the run.

4. Open the "Test-Result.csv" in Excel. You see new test result is appended to the end.

5. Open \fyicenter\jmeter\bin\jmeter.properties in an editor. Then find and update the following line as shown below:

resultcollector.action_if_file_exists=APPEND

The picture below shows you how to append JMeter load test result to old files:

⇒ View Load Test Result Summary

⇐ Save Test Result to File

⇑ Load Testing with JMeter

⇑⇑ Apache JMeter Tutorials