[6.0] 9950f763a Explain how r02976.vtc works

[Dridi Boukelmoune]

commit 9950f763ab6f9da64682a71ab28f226742640324
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Wed Jul 10 11:55:28 2019 +0200

    Explain how r02976.vtc works
    
    It's really not obvious, and if it weren't for other tests covering
    probes it wouldn't be enough by itself to verify what it needs to.

diff --git a/bin/varnishtest/tests/r02976.vtc b/bin/varnishtest/tests/r02976.vtc
index fdfe50fdf..e03383069 100644
--- a/bin/varnishtest/tests/r02976.vtc
+++ b/bin/varnishtest/tests/r02976.vtc
@@ -1,5 +1,9 @@
 varnishtest "Detect probe interval inversion"
 
+# For lack of a better mechanism this test passes by not timing out.
+# This is not enough to guarantee that there wasn't a bug in probe
+# scheduling but it's enough to avoid running into #2976 again.
+
 server s1 -repeat 5 { # probe requests
 	rxreq
 	txresp