FactorBlockDifference type modified, added gtests

test/gtest_factor_block_difference.cpp

@@ -66,6 +66,15 @@ class FixtureFactorBlockDifference : public testing::Test
         virtual void TearDown() override {}
 };
 
+TEST_F(FixtureFactorBlockDifference, CheckFactorType)
+{
+    // Feat_->setMeasurement()
+    FactorBlockDifferencePtr Fac = FactorBase::emplace<FactorBlockDifference>(
+        Feat_, KF0_->getP(), KF1_->getP()
+    );    
+    ASSERT_EQ(Fac->getType(), "FactorBlockDifference");
+}
+
 
 TEST_F(FixtureFactorBlockDifference, EqualP)
 {