Fix error messages and improve documentation

libbeat/tests/integration/elasticsearch_test.go

@@ -116,11 +116,16 @@ func startMockES(t *testing.T, addr string) (*http.Server, metrics.Registry) {
  }
  return true
  },
- time.Second, time.Millisecond, "first server must be up")
+ time.Second, time.Millisecond, "mock-es server did not start on '%s'", addr)
 
  return &s, mr
 }
 
+// waitForEventToBePublished waits for at least one event published
+// by inspecting the count for `bulk.create.total` in `mr`. Once
+// the counter is > 1, waitForEventToBePublished returns. If that
+// does not happen within 10min, then the test fails with a call to
+// t.Fatal.
 func waitForEventToBePublished(t *testing.T, mr metrics.Registry) {
  t.Helper()
  require.Eventually(t, func() bool {