TestRunner log file gets overwritten

When a test case runs using TestRunner and fails the errors are exported to an error log file.

When the same test case runs again, the error log file is overwritten.

When the same test case is used for testing different endpoints and multiple endpoints fail the test, the error log file is overwritten.

Is there a way to either create a unique file for each test case run or ask the TestRunner to append into the error log file?

Thank you.