Add forgotten override keyword

test/gtest_factor_block_difference.cpp

@@ -64,7 +64,7 @@ class FixtureFactorBlockDifference : public testing::Test
             Feat_ = FeatureBase::emplace<FeatureBase>(Cap_, "DIFF", zero3, cov);
         }
 
-        virtual void TearDown(){}
+        virtual void TearDown() override {}
 };