[tools] testbot/TestWTBS: Improve the error checking documentation.

[Francois Gouget]

Signed-off-by: Francois Gouget <fgouget at codeweavers.com>
---
 testbot/tests/TestWTBS | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/testbot/tests/TestWTBS b/testbot/tests/TestWTBS
index 2a6b66e6d..6a19f138b 100755
--- a/testbot/tests/TestWTBS
+++ b/testbot/tests/TestWTBS
@@ -654,14 +654,23 @@ n 0 comm.c:2210: Test failed: WTBS Simulate an unreported test failure
 g 0 tests.report.Report validation errors
 n 0 kernel32:comm has unaccounted for failure messages
 
-This checks that the 'comm.c' failure appears in the 'kernel32' group
-of the reports of all test tasks; that the TestBot issues a report consistency
-failure as well; and that no other new error is present. If no preexisting
-errors are expected, that is if test unit produces no failure when run outside
-the test suite, then one could also issue the following check:
+This checks that the 'comm.c' failure appears in the 'kernel32' group of the
+reports of all test tasks; that the TestBot issues a report consistency
+failure as well; that no other new error is present in either group; and that
+there are no other error groups.
+
+If no preexisting errors are expected, that is if the test unit produces no
+failure when run outside the test suite, then one could also issue the
+following check:
 
 p tests.TestFailures 2
 
+Note that if there is no group directive this test is skipped. So to check that
+there is no error one would declare an empty group such as below, though a
+'TestFailures 0' check seems like a clearer and better approach.
+
+g 0 tests.report.kernel32
+
 Finally, note that while the error directives are inherited by subcategories,
 they are not merged. So if if both win and win32 have error-matching
 directives, win32 will not inherit anything from the win category.
-- 
2.20.1