diff --git a/example/use_block_jacobi_solver_with_default_build.py b/example/use_block_jacobi_solver_with_default_build.py
index 43277f5..cbd40a0 100644
--- a/example/use_block_jacobi_solver_with_default_build.py
+++ b/example/use_block_jacobi_solver_with_default_build.py
@@ -97,7 +97,7 @@
 
     ax1.set_title("cluster at depth 1")
     ax2.set_title("cluster at depth 2")
-    ax4.set_title("Hmatrix on rank 0")
+    ax3.set_title("Hmatrix on rank 0")
     ax4.set_title("Block diagonal Hmatrix on rank 0")
     Htool.plot(ax1, cluster, points, 1)
     Htool.plot(ax2, cluster, points, 2)
diff --git a/src/htool/hmatrix/interfaces/virtual_generator.hpp b/src/htool/hmatrix/interfaces/virtual_generator.hpp
index 20ebaa9..b28c7e6 100644
--- a/src/htool/hmatrix/interfaces/virtual_generator.hpp
+++ b/src/htool/hmatrix/interfaces/virtual_generator.hpp
@@ -47,12 +47,14 @@ class VirtualGeneratorWithPermutationPython : public htool::VirtualGeneratorWith
     VirtualGeneratorWithPermutationPython(const py::array_t<int> &target_permutation, const py::array_t<int> &source_permutation) : VirtualGeneratorWithPermutation<CoefficientPrecision>(target_permutation.data(), source_permutation.data()) {}
 
     void copy_submatrix_from_user_numbering(int M, int N, const int *const rows, const int *const cols, CoefficientPrecision *ptr) const override {
+        if (M * N > 0) {
+            py::array_t<CoefficientPrecision, py::array::f_style> mat(std::array<long int, 2>{M, N}, ptr, py::capsule(ptr));
 
-        py::array_t<CoefficientPrecision, py::array::f_style> mat(std::array<long int, 2>{M, N}, ptr, py::capsule(ptr));
-        py::array_t<int> py_rows(std::array<long int, 2>{M, 1}, rows, py::capsule(rows));
-        py::array_t<int> py_cols(std::array<long int, 2>{N, 1}, cols, py::capsule(cols));
+            py::array_t<int> py_rows(std::array<long int, 2>{M, 1}, rows, py::capsule(rows));
+            py::array_t<int> py_cols(std::array<long int, 2>{N, 1}, cols, py::capsule(cols));
 
-        build_submatrix(py_rows, py_cols, mat);
+            build_submatrix(py_rows, py_cols, mat);
+        }
     }
 
     // lcov does not see it because of trampoline I assume
diff --git a/tests/conftest.py b/tests/conftest.py
index bf86eb6..1d8aac0 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -357,62 +357,3 @@ def load_data_solver(symmetry, mu):
         ovr_subdomain_to_global,
         local_neumann_matrix,
     ]
-
-
-@pytest.fixture(
-    params=[True, False],
-    ids=["block_jacobi_solver", "ddm_solver"],
-)
-def setup_solver_dependencies(request, load_data_solver, epsilon, eta):
-    [
-        A,
-        x_ref,
-        f,
-        cluster,
-        neighbors,
-        intersections,
-        symmetry,
-        UPLO,
-        cluster_to_ovr_subdomain,
-        ovr_subdomain_to_global,
-        local_neumann_matrix,
-    ] = load_data_solver
-
-    generator = GeneratorFromMatrix(cluster.get_permutation(), A)
-    default_approximation = Htool.ComplexDefaultApproximationBuilder(
-        generator,
-        cluster,
-        cluster,
-        epsilon,
-        eta,
-        symmetry,
-        UPLO,
-        mpi4py.MPI.COMM_WORLD,
-    )
-
-    solver = None
-    if request.param:
-        default_solver_builder = Htool.ComplexDefaultSolverBuilder(
-            default_approximation.distributed_operator,
-            default_approximation.block_diagonal_hmatrix,
-        )
-        solver = default_solver_builder.solver
-    else:
-        default_solver_builder = Htool.ComplexDefaultDDMSolverBuilder(
-            default_approximation.distributed_operator,
-            default_approximation.block_diagonal_hmatrix,
-            generator,
-            ovr_subdomain_to_global,
-            cluster_to_ovr_subdomain,
-            neighbors,
-            intersections,
-        )
-        solver = default_solver_builder.solver
-
-    return (
-        solver,
-        x_ref,
-        f,
-        default_approximation.distributed_operator,
-        local_neumann_matrix,
-    )
diff --git a/tests/test_ddm_solver.py b/tests/test_ddm_solver.py
index f9013e5..5a0c5f3 100644
--- a/tests/test_ddm_solver.py
+++ b/tests/test_ddm_solver.py
@@ -124,7 +124,7 @@ def test_ddm_solver(
         + restart
         + " -hpddm_schwarz_method "
         + hpddm_schwarz_method
-        + " -hpddm_max_it 200 -hpddm_variant right -hpddm_compute_residual l2 -hpddm_tol "
+        + " -hpddm_max_it 200 -hpddm_variant right -hpddm_tol "
         + str(tol)
     )
 
diff --git a/tests/test_hmatrix.py b/tests/test_hmatrix.py
deleted file mode 100644
index 2b00194..0000000
--- a/tests/test_hmatrix.py
+++ /dev/null
@@ -1,4 +0,0 @@
-import mpi4py
-import pytest
-
-import Htool