[tracker/sam/functional-tests-quiet: 14/15] squash! WIP: functional-tests: Start daemons through D-Bus autolaunch

[Sam Thursfield <sthursfield src gnome org>]

commit a21017784b798b950587c992de9b44cb34acd80b
Author: Sam Thursfield <sam afuera me uk>
Date:   Thu Aug 29 19:25:34 2019 +0300

    squash! WIP: functional-tests: Start daemons through D-Bus autolaunch
    
    Document the variables which control logging in HACKING.md.

 HACKING.md | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
---
diff --git a/HACKING.md b/HACKING.md
index 89ef319ce..e8d3dcf62 100644
--- a/HACKING.md
+++ b/HACKING.md
@@ -1,3 +1,30 @@
+# Logging
+
+The following environment variables control logging from Tracker daemons:
+
+  * `TRACKER_VERBOSITY`: takes a value of 1, 2 or 3 and causes increasing
+    amounts of log output from Tracker code to be written to stdout.
+  * `G_MESSAGES_DEBUG`: controls log output from GLib-based libraries that
+    are used in the Tracker process. Use `G_MESSAGES_DEBUG=all` for maximal
+    log output.
+
+Internally, Tracker will set `G_MESSAGES_DEBUG=Tracker` if `TRACKER_VERBOSITY`
+is set and `G_MESSAGES_DEBUG` is not set, to enable printing of its own log
+messages to stdout.
+
+You can set these variables when using `tracker-sandbox`, and when running the
+Tracker test suite. Note that Meson will not print log output from tests by
+default, use `meson test --verbose` or `meson test --print-errorlogs` to
+enable.
+
+The functional tests understand an additional variable, `TRACKER_TESTS_VERBOSE`
+with can be set to `1` or `yes` to see detailed logging from the test harness
+itself, and full log output from the internal D-Bus daemon. By default, these
+tests filter output from the D-Bus daemon to only show log messages from
+Tracker processes. Anything written directly to stdout, for example by
+`g_print()` or by the dbus-daemon itself, will not be displayed unless
+`TRACKER_TESTS_VERBOSE` is set.
+
 # Attaching a debugger to Tracker daemons
 
 Tracker daemons are not started directly. Instead they are started by the D-Bus