silence_test: better unit test to detect deadlocks

silence/silence_test.go

@@ -201,12 +201,22 @@ func TestSilencesSetSilence(t *testing.T) {
 	s.gossip = &mockGossip{
 		broadcast: func(d mesh.GossipData) {
 			data, ok := d.(*gossipData)
+
+			// Double check that we can take a lock on s.mtx here.
+			s.mtx.Lock()
+			defer s.mtx.Unlock()
+
 			require.True(t, ok, "gossip data of unknown type")
-			require.Equal(t, want, data, "unexpected gossip broadcast data")
+			require.Equal(t, want.data, data.data, "unexpected gossip broadcast data")
 			close(done)
 		},
 	}
+
+	// setSilence() is always called with s.mtx locked()
+	s.mtx.Lock()
 	require.NoError(t, s.setSilence(sil))
+	s.mtx.Unlock()
+
 	require.Equal(t, want.data, s.st.data, "Unexpected silence state")
 
 	// GossipBroadcast is called in a goroutine.