doc: Update docs on generating simple tests

Refs #235

doc/testing.txt

@@ -234,13 +234,10 @@ Maintenance
 Adding a completion test
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
-You can run `cd test && ./generate cmd` to add a test for the `cmd` command.
-This will add two files with a very basic tests:
-----------------------------------
-test/completion/cmd.exp
-test/lib/completions/cmd.exp
-----------------------------------
-Place any additional tests into `test/lib/completions/cmd.exp`.
+You can run `cd test && ./generate cmd` to add a test for the `cmd`
+command. Additional arguments will be passed to the first generated test case.
+This will add the `test/t/test_cmd.py` file with a very basic test, and add it
+to `test/t/Makefile.am`. Add additional tests to the generated file.
 
 
 Fixing a completion test