📝 Clarify the need for mix_stderr when accessing the output of stderr in tests (#1045)

Co-authored-by: Sofie Van Landeghem <svlandeg@users.noreply.github.com>

Author: mrchrisadams

docs/tutorial/testing.md

@@ -71,7 +71,7 @@ Then we check that the text printed to "standard output" contains the text that
 
 /// tip
 
-You could also check `result.stderr` for "standard error" independently from "standard output" if your `CliRunner` instance is created with the `mix_stderr=False` argument.
+You could also check output sent to "standard error" (`stderr`) instead of "standard output" (`stdout`). To do so, make sure your `CliRunner` instance is created with the `mix_stderr=False` argument. You need this setting to be able to access `result.stderr` in tests.
 
 ///