diff --git a/cpptests/test_fixation_pruning_during_simulation.cc b/cpptests/test_fixation_pruning_during_simulation.cc
index e2d82577c..2ce37003a 100644
--- a/cpptests/test_fixation_pruning_during_simulation.cc
+++ b/cpptests/test_fixation_pruning_during_simulation.cc
@@ -29,6 +29,19 @@
 #include "fwdpy11/mutation_dominance/MutationDominance.hpp"
 #include "fwdpy11/regions/Sregion.hpp"
 
+fwdpy11::MutationRegions
+strong_positive_selection()
+{
+    auto nweights = std::vector<double>();
+    auto sweights = std::vector<double>(1.);
+    std::vector<std::unique_ptr<fwdpy11::Sregion>> nregions, sregions;
+
+    sregions.emplace_back(fwdpy11::ExpS(fwdpy11::Region(0., 10., 1.0, true, 0),
+                                                2.0, 0.025, fwdpy11::fixed_dominance(1.))
+                                      .clone());
+    return fwdpy11::MutationRegions::create(0., nweights, sweights, nregions, sregions);
+}
+
 struct common_setup
 {
     fwdpy11::GSLrng_t rng;
@@ -45,7 +58,7 @@ struct common_setup
     evolve_with_tree_sequences_options options;
 
     common_setup()
-        : rng{42}, pop{100, 10.0}, mregions{{}, {}},
+        : rng{42}, pop{100, 10.0}, mregions{strong_positive_selection()},
           //mregions{fwdpy11::MutationRegions::create(
           //    0, std::vector<double>(), std::vector<double>(1.), {},
           //    std::vector<std::unique_ptr<fwdpy11::Sregion>>(
@@ -78,22 +91,13 @@ BOOST_FIXTURE_TEST_CASE(test_remove_fixations, common_setup)
         = [](const fwdpy11::DiploidPopulation &, fwdpy11::SampleRecorder &) {
 
           };
-    mregions.weights.emplace_back(1.);
-    mregions.regions.emplace_back(fwdpy11::ExpS(fwdpy11::Region(0., 10., 1.0, true, 0),
-                                                2.0, 0.025, fwdpy11::fixed_dominance(1.))
-                                      .clone());
-    auto nw = std::vector<double>();
-    auto nregions = std::vector<std::unique_ptr<fwdpy11::Sregion>>();
-    auto mr = fwdpy11::MutationRegions::create(
-        0., nw, mregions.weights,
-        nregions, mregions.regions);
     BOOST_REQUIRE_EQUAL(mregions.weights.size(), mregions.regions.size());
     BOOST_REQUIRE_EQUAL(mregions.weights.size(), 1);
     options.track_mutation_counts_during_sim = true;
     BOOST_REQUIRE_EQUAL(options.preserve_selected_fixations, false);
     BOOST_REQUIRE_EQUAL(options.track_mutation_counts_during_sim, true);
-    evolve_with_tree_sequences(rng, pop, recorder, 10, forward_demes_graph, 1000, 0., 0.02,
-                               mr, recregions, gvalue_ptrs,
+    evolve_with_tree_sequences(rng, pop, recorder, 10, forward_demes_graph, 1000, 0.,
+                               0.02, mregions, recregions, gvalue_ptrs,
                                sample_recorder_callback, stopping_criterion,
                                post_simplification_recorder, options);
     BOOST_REQUIRE_EQUAL(pop.generation, 1000);