logging: Use /dev/null as test filter
By using this filter for sink tests, we avoid Stackdriver trying to
export any logs during an integration test run.
@@ -34,7 +34,8 @@ import (
var sinkIDs = uid.NewSpace("GO-CLIENT-TEST-SINK", nil)
-const testFilter = ""
+// testFilter matches no logs to avoid exporting anything into the sinks.
+const testFilter = `textPayload="/dev/null"`
var testSinkDestination string
