Fix tests by consuming an initial log entry

Summary: Starting an LFS server seems to implicitly send a health check request. The timing of it is a bit random, enough to make the test flaky. We don't care about it for the purposes of this test, so just wait for it, consume it and ignore it.

Reviewed By: mitrandir77

Differential Revision: D55012938

fbshipit-source-id: dfda3338cdbfe643c0568894e5e34f2e26b39493

eden/mononoke/tests/integration/test-lfs-server-health-checks-failure.t

@@ -36,6 +36,11 @@
   > EOF
   $ lfs_root="$(CACHE_ARGS=--cache-mode=disabled lfs_server --log "$lfs_log" --always-wait-for-upstream --scuba-dataset "file://$SCUBA" --live-config "$(get_configerator_relative_path "${LIVE_CONFIG}")")"
 
+# `lfs_server` sends a health check request (via `lfs_health`), which will emit
+# a (sampled) log entry. In most cases that's ok, and logs are sample anyway.
+# This test requires unsampled Scuba logs and cares about each one of them,
+# so we have to consume.
+  $ wait_for_json_record_count "$SCUBA" 1
 
 # Send a health check request
   $ truncate -s 0 "$SCUBA"

eden/mononoke/tests/integration/test-lfs-server-health-checks-success.t

@@ -30,6 +30,11 @@
   > EOF
   $ lfs_root="$(CACHE_ARGS=--cache-mode=disabled lfs_server --log "$lfs_log" --always-wait-for-upstream --scuba-dataset "file://$SCUBA")"
 
+# `lfs_server` sends a health check request (via `lfs_health`), which will emit
+# a (sampled) log entry. In most cases that's ok, and logs are sample anyway.
+# This test requires unsampled Scuba logs and cares about each one of them,
+# so we have to consume.
+  $ wait_for_json_record_count "$SCUBA" 1
 
 # Send a health check request
   $ truncate -s 0 "$SCUBA"