Merge branch 'jc/refer-to-t-readme-from-submitting-patches'

* jc/refer-to-t-readme-from-submitting-patches:
  t/README: justify why "! grep foo" is sufficient
  SubmittingPatches: refer to t/README for tests

Documentation/SubmittingPatches

@@ -57,7 +57,8 @@ change, the approach taken by the change, and if relevant how this
 differs substantially from the prior version, are all good things
 to have.
 
-Make sure that you have tests for the bug you are fixing.
+Make sure that you have tests for the bug you are fixing.  See
+t/README for guidance.
 
 When adding a new feature, make sure that you have new tests to show
 the feature triggers the new behaviour when it should, and to show the

t/README

@@ -418,7 +418,8 @@ Don't:
    dies in an unexpected way (e.g. segfault).
 
    On the other hand, don't use test_must_fail for running regular
-   platform commands; just use '! cmd'.
+   platform commands; just use '! cmd'.  We are not in the business
+   of verifying that the world given to us sanely works.
 
  - use perl without spelling it as "$PERL_PATH". This is to help our
    friends on Windows where the platform Perl often adds CR before