test/sparse: test full zero matrices

unittest/python/test_sparse_matrix.py

@@ -16,8 +16,7 @@ assert m.toarray() == np.array([2])
 v = sparse_matrix.vector1x1(2)
 assert v.toarray() == np.array([2])
 
-size = 100
-diag_values = np.random.rand(100)
+diag_values = np.random.rand(10)
 diag_mat = sparse_matrix.diagonal(diag_values)
 assert (diag_mat.toarray() == np.diag(diag_values)).all()
 
@@ -26,3 +25,8 @@ assert (diag_mat_copy != diag_mat).nnz == 0
 
 diag_mat_csr = csr_matrix(diag_mat)
 assert (sparse_matrix.copy(diag_mat_csr) != diag_mat_csr).nnz == 0
+
+# test zero matrix
+zero_mat = csr_matrix(np.zeros((10, 1)))
+zero_mat_copy = sparse_matrix.copy(zero_mat)
+assert (zero_mat_copy != zero_mat).nnz == 0