The minimum Armadillo requirement is now 3.6.0.

So the ifdefs aren't necessary.

src/mlpack/tests/tree_test.cpp

@@ -1470,12 +1470,6 @@ void GenerateVectorOfTree(TreeType* node,
   return;
 }
 
-#ifdef ARMA_HAS_SPMAT
-// Only run sparse tree tests if we are using Armadillo 3.6.  Armadillo 3.4 has
-// some bugs that cause the kd-tree splitting procedure to fail terribly.  Soon,
-// that version will be obsolete, though.
-#if !((ARMA_VERSION_MAJOR == 3) && (ARMA_VERSION_MINOR == 4))
-
 /**
  * Exhaustive sparse kd-tree test based on #125.
  *
@@ -1561,9 +1555,6 @@ BOOST_AUTO_TEST_CASE(ExhaustiveSparseKDTreeTest)
   TreeType root(dataset);
 }
 
-#endif // Using Armadillo 3.4.
-#endif // ARMA_HAS_SPMAT
-
 BOOST_AUTO_TEST_CASE(BinarySpaceTreeMoveConstructorTest)
 {
   arma::mat dataset(5, 1000);