diff --git a/CMakeLists.txt b/CMakeLists.txt
index b57f05f..3c0d03a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -275,7 +275,7 @@ else()
 
 if(CMAKE_BUILD_TYPE STREQUAL "Release")
     message(STATUS "Release build")
-    target_compile_options(aare_compiler_flags INTERFACE -O3)
+    target_compile_options(aare_compiler_flags INTERFACE -O3 -g)
 else()
     message(STATUS "Debug build")
 endif()
@@ -426,6 +426,7 @@ if(AARE_TESTS)
             ${CMAKE_CURRENT_SOURCE_DIR}/src/Cluster.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/CalculateEta.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/ClusterFile.test.cpp
+            ${CMAKE_CURRENT_SOURCE_DIR}/src/ClusterFinderMT.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/Pedestal.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/JungfrauDataFile.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/NumpyFile.test.cpp
diff --git a/include/aare/ClusterCollector.hpp b/include/aare/ClusterCollector.hpp
index cb49f58..ae78a8e 100644
--- a/include/aare/ClusterCollector.hpp
+++ b/include/aare/ClusterCollector.hpp
@@ -37,7 +37,11 @@ class ClusterCollector {
   public:
     ClusterCollector(ClusterFinderMT<ClusterType, uint16_t, double> *source) {
         m_source = source->sink();
-        m_thread = std::thread(&ClusterCollector::process, this);
+        m_thread =
+            std::thread(&ClusterCollector::process,
+                        this); // only one process does that so why isnt it
+                               // automatically written to m_cluster in collect
+                               // - instead of writing first to m_sink?
     }
     void stop() {
         m_stop_requested = true;
diff --git a/include/aare/ClusterFinderMT.hpp b/include/aare/ClusterFinderMT.hpp
index 29fc715..2dfb279 100644
--- a/include/aare/ClusterFinderMT.hpp
+++ b/include/aare/ClusterFinderMT.hpp
@@ -34,6 +34,7 @@ template <typename ClusterType = Cluster<int32_t, 3, 3>,
           typename FRAME_TYPE = uint16_t, typename PEDESTAL_TYPE = double>
 class ClusterFinderMT {
 
+  protected:
     using CT = typename ClusterType::value_type;
     size_t m_current_thread{0};
     size_t m_n_threads{0};
@@ -50,6 +51,7 @@ class ClusterFinderMT {
     std::thread m_collect_thread;
     std::chrono::milliseconds m_default_wait{1};
 
+  private:
     std::atomic<bool> m_stop_requested{false};
     std::atomic<bool> m_processing_threads_stopped{true};
 
@@ -120,6 +122,7 @@ class ClusterFinderMT {
     ClusterFinderMT(Shape<2> image_size, PEDESTAL_TYPE nSigma = 5.0,
                     size_t capacity = 2000, size_t n_threads = 3)
         : m_n_threads(n_threads) {
+
         for (size_t i = 0; i < n_threads; i++) {
             m_cluster_finders.push_back(
                 std::make_unique<
diff --git a/src/ClusterFinderMT.test.cpp b/src/ClusterFinderMT.test.cpp
new file mode 100644
index 0000000..9289592
--- /dev/null
+++ b/src/ClusterFinderMT.test.cpp
@@ -0,0 +1,99 @@
+
+#include "aare/ClusterFinderMT.hpp"
+#include "aare/Cluster.hpp"
+#include "aare/ClusterCollector.hpp"
+#include "aare/File.hpp"
+
+#include "test_config.hpp"
+
+#include <catch2/catch_test_macros.hpp>
+#include <filesystem>
+#include <memory>
+
+using namespace aare;
+
+// wrapper function to access private member variables for testing
+template <typename ClusterType, typename FRAME_TYPE = uint16_t,
+          typename PEDESTAL_TYPE = double>
+class ClusterFinderMTWrapper
+    : public ClusterFinderMT<ClusterType, FRAME_TYPE, PEDESTAL_TYPE> {
+
+  public:
+    ClusterFinderMTWrapper(Shape<2> image_size, PEDESTAL_TYPE nSigma = 5.0,
+                           size_t capacity = 2000, size_t n_threads = 3)
+        : ClusterFinderMT<ClusterType, FRAME_TYPE, PEDESTAL_TYPE>(
+              image_size, nSigma, capacity, n_threads) {}
+
+    size_t get_m_input_queues_size() const {
+        return this->m_input_queues.size();
+    }
+
+    size_t get_m_output_queues_size() const {
+        return this->m_output_queues.size();
+    }
+
+    size_t get_m_cluster_finders_size() const {
+        return this->m_cluster_finders.size();
+    }
+
+    bool m_output_queues_are_empty() const {
+        for (auto &queue : this->m_output_queues) {
+            if (!queue->isEmpty())
+                return false;
+        }
+        return true;
+    }
+
+    bool m_input_queues_are_empty() const {
+        for (auto &queue : this->m_input_queues) {
+            if (!queue->isEmpty())
+                return false;
+        }
+        return true;
+    }
+
+    bool m_sink_is_empty() const { return this->m_sink.isEmpty(); }
+
+    size_t m_sink_size() const { return this->m_sink.sizeGuess(); }
+};
+
+TEST_CASE("multithreaded cluster finder", "[.files][.ClusterFinder]") {
+    auto fpath = "/mnt/sls_det_storage/matterhorn_data/aare_test_data/"
+                 "Moench03new/cu_half_speed_master_4.json";
+
+    File file(fpath);
+
+    size_t n_threads = 2;
+    size_t n_frames_pd = 10;
+
+    using ClusterType = Cluster<int32_t, 3, 3>;
+
+    ClusterFinderMTWrapper<ClusterType> cf(
+        {static_cast<int64_t>(file.rows()), static_cast<int64_t>(file.cols())},
+        5, 2000, n_threads); // no idea what frame type is!!! default uint16_t
+
+    CHECK(cf.get_m_input_queues_size() == n_threads);
+    CHECK(cf.get_m_output_queues_size() == n_threads);
+    CHECK(cf.get_m_cluster_finders_size() == n_threads);
+    CHECK(cf.m_output_queues_are_empty() == true);
+    CHECK(cf.m_input_queues_are_empty() == true);
+
+    for (size_t i = 0; i < n_frames_pd; ++i) {
+        cf.find_clusters(file.read_frame().view<uint16_t>());
+    }
+
+    cf.stop();
+
+    CHECK(cf.m_output_queues_are_empty() == true);
+    CHECK(cf.m_input_queues_are_empty() == true);
+
+    CHECK(cf.m_sink_size() == n_frames_pd);
+    ClusterCollector<ClusterType> clustercollector(&cf);
+
+    clustercollector.stop();
+
+    CHECK(cf.m_sink_size() == 0);
+
+    auto clustervec = clustercollector.steal_clusters();
+    // CHECK(clustervec.size() == ) //dont know how many clusters to expect
+}