diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
new file mode 100644
index 00000000000..5924a06d087
--- /dev/null
+++ b/.pre-commit-config.yaml
@@ -0,0 +1,12 @@
+repos:
+  - repo: https://github.com/pre-commit/mirrors-clang-format
+    rev: 'v14.0.0'
+    hooks:
+      - id: clang-format
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v3.2.0
+    hooks:
+    - id: trailing-whitespace
+    - id: end-of-file-fixer
+    - id: check-yaml
+    - id: check-added-large-files
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/GenerateParameters.hpp b/Core/include/Acts/EventData/detail/GenerateParameters.hpp
similarity index 97%
rename from Tests/CommonHelpers/Acts/Tests/CommonHelpers/GenerateParameters.hpp
rename to Core/include/Acts/EventData/detail/GenerateParameters.hpp
index c9e4cd793b8..955d92e15fe 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/GenerateParameters.hpp
+++ b/Core/include/Acts/EventData/detail/GenerateParameters.hpp
@@ -15,8 +15,7 @@
 #include <random>
 #include <utility>
 
-namespace Acts {
-namespace Test {
+namespace Acts::detail::Test {
 
 /// Generate a random parameters vector and covariance matrix.
 ///
@@ -77,5 +76,4 @@ inline auto generateFreeParametersCovariance(generator_t& rng) {
   return generateParametersCovariance<ActsScalar, eFreeSize>(rng);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::detail::Test
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/MultiTrajectoryTestsCommon.hpp b/Core/include/Acts/EventData/detail/MultiTrajectoryTestsCommon.hpp
similarity index 99%
rename from Tests/CommonHelpers/Acts/Tests/CommonHelpers/MultiTrajectoryTestsCommon.hpp
rename to Core/include/Acts/EventData/detail/MultiTrajectoryTestsCommon.hpp
index a64cfa76a64..138d673515f 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/MultiTrajectoryTestsCommon.hpp
+++ b/Core/include/Acts/EventData/detail/MultiTrajectoryTestsCommon.hpp
@@ -13,15 +13,15 @@
 
 #include "Acts/Definitions/TrackParametrization.hpp"
 #include "Acts/EventData/TrackStatePropMask.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
+#include "Acts/EventData/detail/TestTrackState.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
-#include "Acts/Tests/CommonHelpers/TestTrackState.hpp"
 #include "Acts/Utilities/CalibrationContext.hpp"
 #include "Acts/Utilities/HashedString.hpp"
 
 #include <random>
 
-namespace Acts::Test {
+namespace Acts::detail::Test {
 
 template <typename factory_t>
 class MultiTrajectoryTestsCommon {
@@ -376,7 +376,7 @@ class MultiTrajectoryTestsCommon {
     BOOST_CHECK_EQUAL(
         ts.getUncalibratedSourceLink().template get<TestSourceLink>().sourceId,
         ttsb.sourceLink.sourceId);
-    auto m2 = std::get<Measurement<BoundIndices, 2u>>(meas);
+    auto m2 = std::get<Acts::Measurement<BoundIndices, 2u>>(meas);
 
     BOOST_CHECK_EQUAL(ts.calibratedSize(), 2);
     BOOST_CHECK_EQUAL(ts.effectiveCalibrated(), m2.parameters());
@@ -1065,4 +1065,4 @@ class MultiTrajectoryTestsCommon {
     // runTest([](std::string_view c) { return c; });
   }
 };
-}  // namespace Acts::Test
+}  // namespace Acts::detail::Test
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSourceLink.hpp b/Core/include/Acts/EventData/detail/TestSourceLink.hpp
similarity index 84%
rename from Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSourceLink.hpp
rename to Core/include/Acts/EventData/detail/TestSourceLink.hpp
index 3480064f91e..41464682bde 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSourceLink.hpp
+++ b/Core/include/Acts/EventData/detail/TestSourceLink.hpp
@@ -25,8 +25,7 @@
 #include <iosfwd>
 #include <stdexcept>
 
-namespace Acts {
-namespace Test {
+namespace Acts::detail::Test {
 
 /// A minimal source link implementation for testing.
 ///
@@ -69,7 +68,24 @@ struct TestSourceLink final {
   TestSourceLink(TestSourceLink&&) = default;
   TestSourceLink& operator=(const TestSourceLink&) = default;
   TestSourceLink& operator=(TestSourceLink&&) = default;
-
+  bool operator==(const TestSourceLink& rhs) const {
+    return (m_geometryId == rhs.m_geometryId) && (sourceId == rhs.sourceId) &&
+           (indices == rhs.indices) && (parameters == rhs.parameters) &&
+           (covariance == rhs.covariance);
+  }
+  bool operator!=(const TestSourceLink& rhs) const { return !(*this == rhs); }
+  std::ostream& print(std::ostream& os) const {
+    os << "TestsSourceLink(geometryId=" << m_geometryId
+       << ",sourceId=" << sourceId;
+    if (indices[0] != eBoundSize) {
+      os << ",index0=" << indices[0];
+    }
+    if (indices[1] != eBoundSize) {
+      os << ",index1=" << indices[1];
+    }
+    os << ")";
+    return os;
+  }
   constexpr std::size_t index() const { return sourceId; }
 
   struct SurfaceAccessor {
@@ -82,9 +98,10 @@ struct TestSourceLink final {
   };
 };
 
-bool operator==(const TestSourceLink& lhs, const TestSourceLink& rhs);
-bool operator!=(const TestSourceLink& lhs, const TestSourceLink& rhs);
-std::ostream& operator<<(std::ostream& os, const TestSourceLink& sourceLink);
+inline std::ostream& operator<<(std::ostream& os,
+                                const TestSourceLink& sourceLink) {
+  return sourceLink.print(os);
+}
 
 /// Extract the measurement from a TestSourceLink.
 ///
@@ -133,5 +150,4 @@ void testSourceLinkCalibrator(
                                                trackState);
 }
 
-}  // namespace Test
-}  // namespace Acts
+}  // namespace Acts::detail::Test
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestTrackState.hpp b/Core/include/Acts/EventData/detail/TestTrackState.hpp
similarity index 96%
rename from Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestTrackState.hpp
rename to Core/include/Acts/EventData/detail/TestTrackState.hpp
index 7f7b025f680..bf5af9cac88 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestTrackState.hpp
+++ b/Core/include/Acts/EventData/detail/TestTrackState.hpp
@@ -10,13 +10,13 @@
 
 #include "Acts/EventData/TrackParameters.hpp"
 #include "Acts/EventData/VectorMultiTrajectory.hpp"
-#include "Acts/Tests/CommonHelpers/GenerateParameters.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
+#include "Acts/EventData/detail/GenerateParameters.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Utilities/CalibrationContext.hpp"
 
 #include <random>
 
-namespace Acts::Test {
+namespace Acts::detail::Test {
 
 struct TestTrackState {
   std::shared_ptr<Surface> surface;
@@ -132,4 +132,4 @@ void fillTrackState(const TestTrackState& pc, TrackStatePropMask mask,
   }
 }
 
-}  // namespace Acts::Test
+}  // namespace Acts::detail::Test
diff --git a/Core/include/Acts/Seeding/SeedFinderOrthogonal.ipp b/Core/include/Acts/Seeding/SeedFinderOrthogonal.ipp
index b0175523c73..27f32deb424 100644
--- a/Core/include/Acts/Seeding/SeedFinderOrthogonal.ipp
+++ b/Core/include/Acts/Seeding/SeedFinderOrthogonal.ipp
@@ -85,6 +85,10 @@ auto SeedFinderOrthogonal<external_spacepoint_t>::validTupleOrthoRangeLH(
   res[DimPhi].shrinkMin(pL - m_config.deltaPhiMax);
   res[DimPhi].shrinkMax(pL + m_config.deltaPhiMax);
 
+  // Cut: Ensure that z-distance between SPs is within max and min values.
+  res[DimZ].shrinkMin(zL - m_config.deltaZMax);
+  res[DimZ].shrinkMax(zL + m_config.deltaZMax);
+
   return res;
 }
 
@@ -93,6 +97,7 @@ auto SeedFinderOrthogonal<external_spacepoint_t>::validTupleOrthoRangeHL(
     const internal_sp_t &high) const -> typename tree_t::range_t {
   float pM = high.phi();
   float rM = high.radius();
+  float zM = high.z();
 
   typename tree_t::range_t res;
 
@@ -129,13 +134,13 @@ auto SeedFinderOrthogonal<external_spacepoint_t>::validTupleOrthoRangeHL(
    */
   float fracR = res[DimR].min() / rM;
 
-  float zMin = (high.z() - m_config.collisionRegionMin) * fracR +
-               m_config.collisionRegionMin;
-  float zMax = (high.z() - m_config.collisionRegionMax) * fracR +
-               m_config.collisionRegionMax;
+  float zMin =
+      (zM - m_config.collisionRegionMin) * fracR + m_config.collisionRegionMin;
+  float zMax =
+      (zM - m_config.collisionRegionMax) * fracR + m_config.collisionRegionMax;
 
-  res[DimZ].shrinkMin(std::min(zMin, high.z()));
-  res[DimZ].shrinkMax(std::max(zMax, high.z()));
+  res[DimZ].shrinkMin(std::min(zMin, zM));
+  res[DimZ].shrinkMax(std::max(zMax, zM));
 
   /*
    * Cut: Shrink the φ range, such that Δφ_min ≤ φ - φ_H ≤ Δφ_max
@@ -143,6 +148,10 @@ auto SeedFinderOrthogonal<external_spacepoint_t>::validTupleOrthoRangeHL(
   res[DimPhi].shrinkMin(pM - m_config.deltaPhiMax);
   res[DimPhi].shrinkMax(pM + m_config.deltaPhiMax);
 
+  // Cut: Ensure that z-distance between SPs is within max and min values.
+  res[DimZ].shrinkMin(zM - m_config.deltaZMax);
+  res[DimZ].shrinkMax(zM + m_config.deltaZMax);
+
   return res;
 }
 
@@ -219,12 +228,6 @@ bool SeedFinderOrthogonal<external_spacepoint_t>::validTuple(
   if (std::fabs(cotTheta) > m_config.cotThetaMax) {
     return false;
   }
-  /*
-   * Cut: Ensure that z-distance between SPs is within max and min values.
-   */
-  if (std::abs(deltaZ) > m_config.deltaZMax) {
-    return false;
-  }
 
   /*
    * Cut: Ensure that inner-middle dublet is in a certain (r, eta) region of the
diff --git a/Core/include/Acts/TrackFitting/GlobalChiSquareFitter.hpp b/Core/include/Acts/TrackFitting/GlobalChiSquareFitter.hpp
index 6bb62a1d9b4..30eee1c3ad1 100644
--- a/Core/include/Acts/TrackFitting/GlobalChiSquareFitter.hpp
+++ b/Core/include/Acts/TrackFitting/GlobalChiSquareFitter.hpp
@@ -202,8 +202,8 @@ struct Gx2FitterResult {
   // between the first and last measurements.
   std::size_t measurementHoles = 0;
 
-  // Counter for handled states
-  std::size_t processedStates = 0;
+  // Counter for handled measurements
+  std::size_t processedMeasurements = 0;
 
   // Indicator if track fitting has been done
   bool finished = false;
@@ -261,12 +261,12 @@ void collector(typename traj_t::TrackStateProxy& trackStateProxy,
                         predicted)
                            .eval();
 
-  ACTS_VERBOSE("Processing and collecting measurements in Actor:\n"
-               << "\tMeasurement:\t" << measurement.transpose()
-               << "\n\tPredicted:\t" << predicted.transpose()
-               << "\n\tProjector:\t" << trackStateProxy.effectiveProjector()
-               << "\n\tProjected Jacobian:\t" << projJacobian
-               << "\n\tCovariance Measurements:\t" << covarianceMeasurement);
+  ACTS_VERBOSE("Processing and collecting measurements in Actor:"
+               << "\n    Measurement:\t" << measurement.transpose()
+               << "\n    Predicted:\t" << predicted.transpose()
+               << "\n    Projector:\t" << trackStateProxy.effectiveProjector()
+               << "\n    Projected Jacobian:\t" << projJacobian
+               << "\n    Covariance Measurements:\t" << covarianceMeasurement);
 
   // Collect residuals, covariances, and projected jacobians
   for (std::size_t i = 0; i < measDim; i++) {
@@ -280,13 +280,16 @@ void collector(typename traj_t::TrackStateProxy& trackStateProxy,
     result.collectorCovariances.push_back(covarianceMeasurement(i, i));
     result.collectorProjectedJacobians.push_back(projJacobian.row(i));
 
-    ACTS_VERBOSE("\tSplitting the measurement:\n"
-                 << "\t\tResidual:\t" << measurement[i] - projPredicted[i]
-                 << "\n\t\tCovariance:\t" << covarianceMeasurement(i, i)
-                 << "\n\t\tProjected Jacobian:\t" << projJacobian.row(i));
+    ACTS_VERBOSE("    Splitting the measurement:"
+                 << "\n        Residual:\t" << measurement[i] - projPredicted[i]
+                 << "\n        Covariance:\t" << covarianceMeasurement(i, i)
+                 << "\n        Projected Jacobian:\t" << projJacobian.row(i));
   }
 }
 
+BoundVector calculateDeltaParams(bool zeroField, const BoundMatrix& aMatrix,
+                                 const BoundVector& bVector);
+
 /// Global Chi Square fitter (GX2F) implementation.
 ///
 /// @tparam propagator_t Type of the propagation class
@@ -394,26 +397,13 @@ class Gx2Fitter {
         return;
       }
 
-      // Add the measurement surface as external surface to navigator.
-      // We will try to hit those surface by ignoring boundary checks.
-      if constexpr (!isDirectNavigator) {
-        if (result.processedStates == 0) {
-          for (auto measurementIt = inputMeasurements->begin();
-               measurementIt != inputMeasurements->end(); measurementIt++) {
-            navigator.insertExternalSurface(state.navigation,
-                                            measurementIt->first);
-          }
-        }
-      }
-
       // Update:
       // - Waiting for a current surface
       auto surface = navigator.currentSurface(state.navigation);
       //      std::string direction = state.stepping.navDir.toString();
       if (surface != nullptr) {
         ++result.surfaceCount;
-        ACTS_VERBOSE("Measurement surface " << surface->geometryId()
-                                            << " detected.");
+        ACTS_VERBOSE("Surface " << surface->geometryId() << " detected.");
 
         // check if measurement surface
         auto sourcelink_it = inputMeasurements->find(surface->geometryId());
@@ -428,10 +418,10 @@ class Gx2Fitter {
 
           ACTS_VERBOSE(
               "Actor - indices before processing:"
-              << "\n\t"
+              << "\n    "
               << "result.lastMeasurementIndex: " << result.lastMeasurementIndex
-              << "\n\t"
-              << "result.lastTrackIndex: " << result.lastTrackIndex << "\n\t"
+              << "\n    "
+              << "result.lastTrackIndex: " << result.lastTrackIndex << "\n    "
               << "result.fittedStates->size(): " << result.fittedStates->size())
 
           // TODO generalize the update of the currentTrackIndex
@@ -441,38 +431,12 @@ class Gx2Fitter {
           TrackStatePropMask mask =
               ~(TrackStatePropMask::Smoothed | TrackStatePropMask::Filtered);
 
-          // Checks if an existing surface is found during the gx2f-iteration.
-          // If not, a new index will be generated afterwards.
-          // During the first iteration, we will always create a new index.
-          std::size_t currentTrackIndex = Acts::MultiTrajectoryTraits::kInvalid;
-          if (nUpdate == 0) {
-            ACTS_VERBOSE("   processSurface: nUpdate == 0 decision");
-
-            // Add a <mask> TrackState entry multi trajectory. This allocates
-            // storage for all components, which we will set later.
-            currentTrackIndex =
-                fittedStates.addTrackState(mask, result.lastTrackIndex);
-          } else {
-            ACTS_VERBOSE("   processSurface: nUpdate > 0 decision");
-
-            if (result.lastTrackIndex ==
-                Acts::MultiTrajectoryTraits::kInvalid) {
-              currentTrackIndex = 0;
-              ACTS_VERBOSE("   processSurface: currentTrackIndex (kInv->0) = "
-                           << currentTrackIndex);
-            } else if (result.lastTrackIndex < fittedStates.size() - 1) {
-              currentTrackIndex = result.lastTrackIndex + 1;
-              ACTS_VERBOSE("   processSurface: currentTrackIndex (n+1) = "
-                           << currentTrackIndex);
-            } else {
-              // Add a <mask> TrackState entry multi trajectory. This allocates
-              // storage for all components, which we will set later.
-              currentTrackIndex =
-                  fittedStates.addTrackState(mask, result.lastTrackIndex);
-              ACTS_VERBOSE("   processSurface: currentTrackIndex (ADD NEW)= "
-                           << currentTrackIndex);
-            }
-          }
+          ACTS_VERBOSE("    processSurface: addTrackState");
+
+          // Add a <mask> TrackState entry multi trajectory. This allocates
+          // storage for all components, which we will set later.
+          std::size_t currentTrackIndex =
+              fittedStates.addTrackState(mask, result.lastTrackIndex);
 
           // now get track state proxy back
           typename traj_t::TrackStateProxy trackStateProxy =
@@ -532,16 +496,16 @@ class Gx2Fitter {
 
           // Set the measurement type flag
           typeFlags.set(TrackStateFlag::MeasurementFlag);
-          // We count the processed state
-          ++result.processedStates;
+          // We count the processed measurement
+          ++result.processedMeasurements;
           ACTS_VERBOSE("Actor - indices after processing, before over writing:"
-                       << "\n\t"
+                       << "\n    "
                        << "result.lastMeasurementIndex: "
-                       << result.lastMeasurementIndex << "\n\t"
+                       << result.lastMeasurementIndex << "\n    "
                        << "trackStateProxy.index(): " << trackStateProxy.index()
-                       << "\n\t"
+                       << "\n    "
                        << "result.lastTrackIndex: " << result.lastTrackIndex
-                       << "\n\t"
+                       << "\n    "
                        << "currentTrackIndex: " << currentTrackIndex)
           result.lastMeasurementIndex = currentTrackIndex;
           result.lastTrackIndex = currentTrackIndex;
@@ -549,6 +513,13 @@ class Gx2Fitter {
           ACTS_INFO("Actor: This case is not implemented yet")
         }
       }
+      ACTS_DEBUG("result.processedMeasurements: "
+                 << result.processedMeasurements << "\n"
+                 << "inputMeasurements.size()" << inputMeasurements->size())
+      if (result.processedMeasurements >= inputMeasurements->size()) {
+        ACTS_INFO("Actor: finish: all measurements found.");
+        result.finished = true;
+      }
 
       if (result.surfaceCount > 900) {
         ACTS_INFO("Actor: finish due to limit. Result might be garbage.");
@@ -678,6 +649,9 @@ class Gx2Fitter {
 
       auto& r = inputResult.template get<Gx2FitterResult<traj_t>>();
 
+      // Clear the track container. It could be more performant to update the
+      // existing states, but this needs some more thinking.
+      trackContainer.clear();
       r.fittedStates = &trackContainer.trackStateContainer();
       // propagate with params and return jacobians and residuals
       auto result = m_propagator.template propagate(
@@ -718,20 +692,8 @@ class Gx2Fitter {
       }
 
       // calculate delta params [a] * delta = b
-      deltaParams = BoundVector::Zero();
-      if (gx2fOptions.zeroField) {
-        constexpr std::size_t reducedMatrixSize = 4;
-        deltaParams.topLeftCorner<reducedMatrixSize, 1>() =
-            aMatrix.topLeftCorner<reducedMatrixSize, reducedMatrixSize>()
-                .colPivHouseholderQr()
-                .solve(bVector.topLeftCorner<reducedMatrixSize, 1>());
-      } else {
-        constexpr std::size_t reducedMatrixSize = 5;
-        deltaParams.topLeftCorner<reducedMatrixSize, 1>() =
-            aMatrix.topLeftCorner<reducedMatrixSize, reducedMatrixSize>()
-                .colPivHouseholderQr()
-                .solve(bVector.topLeftCorner<reducedMatrixSize, 1>());
-      }
+      deltaParams =
+          calculateDeltaParams(gx2fOptions.zeroField, aMatrix, bVector);
 
       ACTS_VERBOSE("aMatrix:\n"
                    << aMatrix << "\n"
@@ -753,6 +715,11 @@ class Gx2Fitter {
         break;
       }
 
+      // TODO investigate further
+      if (chi2sum > oldChi2sum + 1e-5) {
+        ACTS_DEBUG("chi2 not converging monotonically");
+      }
+
       oldChi2sum = chi2sum;
     }
     ACTS_DEBUG("Finished to iterate");
@@ -822,5 +789,6 @@ class Gx2Fitter {
     return track;
   }
 };
+
 }  // namespace Experimental
 }  // namespace Acts
diff --git a/Core/src/TrackFitting/CMakeLists.txt b/Core/src/TrackFitting/CMakeLists.txt
index 05eccd967ad..c370dc9aa01 100644
--- a/Core/src/TrackFitting/CMakeLists.txt
+++ b/Core/src/TrackFitting/CMakeLists.txt
@@ -9,4 +9,5 @@ target_sources(
     GsfUtils.cpp
     BetheHeitlerApprox.cpp
     GsfMixtureReduction.cpp
+    GlobalChiSquareFitter.cpp
 )
diff --git a/Core/src/TrackFitting/GlobalChiSquareFitter.cpp b/Core/src/TrackFitting/GlobalChiSquareFitter.cpp
new file mode 100644
index 00000000000..c74319982ec
--- /dev/null
+++ b/Core/src/TrackFitting/GlobalChiSquareFitter.cpp
@@ -0,0 +1,34 @@
+// This file is part of the Acts project.
+//
+// Copyright (C) 2023 CERN for the benefit of the Acts project
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include "Acts/TrackFitting/GlobalChiSquareFitter.hpp"
+
+#include "Acts/Definitions/TrackParametrization.hpp"
+
+namespace Acts::Experimental {
+
+BoundVector calculateDeltaParams(bool zeroField, const BoundMatrix& aMatrix,
+                                 const BoundVector& bVector) {
+  BoundVector deltaParams = BoundVector::Zero();
+  if (zeroField) {
+    constexpr std::size_t reducedMatrixSize = 4;
+    deltaParams.topLeftCorner<reducedMatrixSize, 1>() =
+        aMatrix.topLeftCorner<reducedMatrixSize, reducedMatrixSize>()
+            .colPivHouseholderQr()
+            .solve(bVector.topLeftCorner<reducedMatrixSize, 1>());
+  } else {
+    constexpr std::size_t reducedMatrixSize = 5;
+    deltaParams.topLeftCorner<reducedMatrixSize, 1>() =
+        aMatrix.topLeftCorner<reducedMatrixSize, reducedMatrixSize>()
+            .colPivHouseholderQr()
+            .solve(bVector.topLeftCorner<reducedMatrixSize, 1>());
+  }
+
+  return deltaParams;
+}
+}  // namespace Acts::Experimental
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/MeasurementsCreator.hpp b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/MeasurementsCreator.hpp
index b18fff83d49..9a20f419cdd 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/MeasurementsCreator.hpp
+++ b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/MeasurementsCreator.hpp
@@ -10,13 +10,13 @@
 
 #include "Acts/Definitions/Units.hpp"
 #include "Acts/EventData/Measurement.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Geometry/GeometryHierarchyMap.hpp"
 #include "Acts/MagneticField/MagneticFieldContext.hpp"
 #include "Acts/Propagator/AbortList.hpp"
 #include "Acts/Propagator/ActionList.hpp"
 #include "Acts/Propagator/StandardAborters.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
 #include "Acts/Utilities/Logger.hpp"
 
 #include <memory>
@@ -46,8 +46,8 @@ using MeasurementResolutionMap =
 
 /// Result struct for generated measurements and outliers.
 struct Measurements {
-  std::vector<TestSourceLink> sourceLinks;
-  std::vector<TestSourceLink> outlierSourceLinks;
+  std::vector<Acts::detail::Test::TestSourceLink> sourceLinks;
+  std::vector<Acts::detail::Test::TestSourceLink> outlierSourceLinks;
   std::vector<BoundVector> truthParameters;
 };
 
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSourceLink.cpp b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSourceLink.cpp
deleted file mode 100644
index 7879edfdf3c..00000000000
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSourceLink.cpp
+++ /dev/null
@@ -1,38 +0,0 @@
-// This file is part of the Acts project.
-//
-// Copyright (C) 2020 CERN for the benefit of the Acts project
-//
-// This Source Code Form is subject to the terms of the Mozilla Public
-// License, v. 2.0. If a copy of the MPL was not distributed with this
-// file, You can obtain one at http://mozilla.org/MPL/2.0/.
-
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
-
-#include <ostream>
-
-bool Acts::Test::operator==(const TestSourceLink& lhs,
-                            const TestSourceLink& rhs) {
-  return (lhs.m_geometryId == rhs.m_geometryId) &&
-         (lhs.sourceId == rhs.sourceId) && (lhs.indices == rhs.indices) &&
-         (lhs.parameters == rhs.parameters) &&
-         (lhs.covariance == rhs.covariance);
-}
-
-bool Acts::Test::operator!=(const TestSourceLink& lhs,
-                            const TestSourceLink& rhs) {
-  return !(lhs == rhs);
-}
-
-std::ostream& Acts::Test::operator<<(
-    std::ostream& os, const Acts::Test::TestSourceLink& sourceLink) {
-  os << "TestsSourceLink(geometryId=" << sourceLink.m_geometryId
-     << ",sourceId=" << sourceLink.sourceId;
-  if (sourceLink.indices[0] != eBoundSize) {
-    os << ",index0=" << sourceLink.indices[0];
-  }
-  if (sourceLink.indices[1] != eBoundSize) {
-    os << ",index1=" << sourceLink.indices[1];
-  }
-  os << ")";
-  return os;
-}
diff --git a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSpacePoint.hpp b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSpacePoint.hpp
index 2856dbecd6b..45c50acc0a1 100644
--- a/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSpacePoint.hpp
+++ b/Tests/CommonHelpers/Acts/Tests/CommonHelpers/TestSpacePoint.hpp
@@ -69,12 +69,13 @@ class TestSpacePoint {
 };
 
 inline bool operator==(const TestSpacePoint& lhs, const TestSpacePoint& rhs) {
-  return (std::equal(lhs.sourceLinks().begin(), lhs.sourceLinks().end(),
-                     rhs.sourceLinks().begin(),
-                     [](const auto& lsl, const auto& rsl) {
-                       return lsl.template get<TestSourceLink>() ==
-                              rsl.template get<TestSourceLink>();
-                     }) &&
+  return (std::equal(
+              lhs.sourceLinks().begin(), lhs.sourceLinks().end(),
+              rhs.sourceLinks().begin(),
+              [](const auto& lsl, const auto& rsl) {
+                return lsl.template get<Acts::detail::Test::TestSourceLink>() ==
+                       rsl.template get<Acts::detail::Test::TestSourceLink>();
+              }) &&
           lhs.x() == rhs.x()) &&
          (lhs.y() == rhs.y()) && (lhs.z() == rhs.z()) &&
          (lhs.varianceR() == rhs.varianceR()) &&
diff --git a/Tests/CommonHelpers/CMakeLists.txt b/Tests/CommonHelpers/CMakeLists.txt
index 3bf427e6af9..fc09c3e5ffa 100644
--- a/Tests/CommonHelpers/CMakeLists.txt
+++ b/Tests/CommonHelpers/CMakeLists.txt
@@ -4,7 +4,6 @@ file(TO_NATIVE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/../Data" acts_test_data_dir)
 add_library(
   ActsTestsCommonHelpers SHARED
   Acts/Tests/CommonHelpers/DataDirectory.cpp
-  Acts/Tests/CommonHelpers/TestSourceLink.cpp
 )
 target_compile_definitions(
   ActsTestsCommonHelpers
diff --git a/Tests/UnitTests/Alignment/Kernel/AlignmentTests.cpp b/Tests/UnitTests/Alignment/Kernel/AlignmentTests.cpp
index a536f43a811..3acf3133c3c 100644
--- a/Tests/UnitTests/Alignment/Kernel/AlignmentTests.cpp
+++ b/Tests/UnitTests/Alignment/Kernel/AlignmentTests.cpp
@@ -10,6 +10,7 @@
 
 #include "Acts/Definitions/Units.hpp"
 #include "Acts/EventData/TrackParameters.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Geometry/CuboidVolumeBounds.hpp"
 #include "Acts/Geometry/CuboidVolumeBuilder.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
@@ -34,7 +35,6 @@
 #include "Acts/Tests/CommonHelpers/FloatComparisons.hpp"
 #include "Acts/Tests/CommonHelpers/MeasurementsCreator.hpp"
 #include "Acts/Tests/CommonHelpers/PredefinedMaterials.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
 #include "Acts/TrackFitting/GainMatrixSmoother.hpp"
 #include "Acts/TrackFitting/GainMatrixUpdater.hpp"
 #include "Acts/TrackFitting/KalmanFitter.hpp"
@@ -50,6 +50,7 @@ namespace {
 using namespace Acts;
 using namespace ActsAlignment;
 using namespace Acts::Test;
+using namespace Acts::detail::Test;
 using namespace Acts::UnitLiterals;
 
 using StraightPropagator =
diff --git a/Tests/UnitTests/Core/EventData/MeasurementTests.cpp b/Tests/UnitTests/Core/EventData/MeasurementTests.cpp
index 28efe7ad43c..2edff964c89 100644
--- a/Tests/UnitTests/Core/EventData/MeasurementTests.cpp
+++ b/Tests/UnitTests/Core/EventData/MeasurementTests.cpp
@@ -13,9 +13,9 @@
 #include "Acts/Definitions/TrackParametrization.hpp"
 #include "Acts/EventData/Measurement.hpp"
 #include "Acts/EventData/SourceLink.hpp"
+#include "Acts/EventData/detail/GenerateParameters.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Tests/CommonHelpers/FloatComparisons.hpp"
-#include "Acts/Tests/CommonHelpers/GenerateParameters.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
 
 #include <algorithm>
 #include <array>
@@ -28,8 +28,8 @@
 #include <vector>
 
 using namespace Acts;
-using namespace Acts::Test;
-using SourceLink = Acts::Test::TestSourceLink;
+using namespace Acts::detail::Test;
+using SourceLink = Acts::detail::Test::TestSourceLink;
 namespace bd = boost::unit_test::data;
 
 namespace {
diff --git a/Tests/UnitTests/Core/EventData/MultiTrajectoryTests.cpp b/Tests/UnitTests/Core/EventData/MultiTrajectoryTests.cpp
index 72d808cfba8..2cb2ecbe82c 100644
--- a/Tests/UnitTests/Core/EventData/MultiTrajectoryTests.cpp
+++ b/Tests/UnitTests/Core/EventData/MultiTrajectoryTests.cpp
@@ -17,12 +17,12 @@
 #include "Acts/EventData/TrackParameters.hpp"
 #include "Acts/EventData/TrackStatePropMask.hpp"
 #include "Acts/EventData/VectorMultiTrajectory.hpp"
+#include "Acts/EventData/detail/MultiTrajectoryTestsCommon.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
+#include "Acts/EventData/detail/TestTrackState.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Geometry/GeometryIdentifier.hpp"
 #include "Acts/Tests/CommonHelpers/FloatComparisons.hpp"
-#include "Acts/Tests/CommonHelpers/MultiTrajectoryTestsCommon.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
-#include "Acts/Tests/CommonHelpers/TestTrackState.hpp"
 
 #include <algorithm>
 #include <array>
@@ -40,6 +40,7 @@ namespace {
 using namespace Acts;
 using namespace Acts::UnitLiterals;
 using namespace Acts::Test;
+using namespace Acts::detail::Test;
 namespace bd = boost::unit_test::data;
 
 using ParametersVector = BoundTrackParameters::ParametersVector;
diff --git a/Tests/UnitTests/Core/EventData/SourceLinkTests.cpp b/Tests/UnitTests/Core/EventData/SourceLinkTests.cpp
index 40b788f40f1..6f017b4c0c3 100644
--- a/Tests/UnitTests/Core/EventData/SourceLinkTests.cpp
+++ b/Tests/UnitTests/Core/EventData/SourceLinkTests.cpp
@@ -10,14 +10,31 @@
 
 #include "Acts/Definitions/Units.hpp"
 #include "Acts/EventData/SourceLink.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Geometry/GeometryIdentifier.hpp"
 
 #include <any>
+#include <sstream>
 
 using namespace Acts::UnitLiterals;
 
 BOOST_AUTO_TEST_SUITE(EventDataSourceLink)
 
+BOOST_AUTO_TEST_CASE(TestSourceLinkCoverage) {
+  using Acts::detail::Test::TestSourceLink;
+  TestSourceLink ts;
+  Acts::Vector2 stddev(0.01, 0.1);
+  Acts::SquareMatrix2 cov = stddev.cwiseProduct(stddev).asDiagonal();
+  TestSourceLink l1(Acts::eBoundLoc0, 0.1, cov(0, 0),
+                    Acts::GeometryIdentifier(0x999), 0);
+  TestSourceLink l2(l1);
+
+  BOOST_CHECK(l1 == l2);     // testing the ==
+  BOOST_CHECK(!(l1 != l2));  // testing the !=
+  std::ostringstream str;
+  str << l1;
+}
+
 struct MySourceLink {
   Acts::GeometryIdentifier m_geometryId;
 
diff --git a/Tests/UnitTests/Core/EventData/TrackTests.cpp b/Tests/UnitTests/Core/EventData/TrackTests.cpp
index 5dad757f80b..af75fc0be0d 100644
--- a/Tests/UnitTests/Core/EventData/TrackTests.cpp
+++ b/Tests/UnitTests/Core/EventData/TrackTests.cpp
@@ -19,11 +19,11 @@
 #include "Acts/EventData/TrackStatePropMask.hpp"
 #include "Acts/EventData/VectorMultiTrajectory.hpp"
 #include "Acts/EventData/VectorTrackContainer.hpp"
+#include "Acts/EventData/detail/GenerateParameters.hpp"
+#include "Acts/EventData/detail/TestTrackState.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Surfaces/PlaneSurface.hpp"
 #include "Acts/Surfaces/Surface.hpp"
-#include "Acts/Tests/CommonHelpers/GenerateParameters.hpp"
-#include "Acts/Tests/CommonHelpers/TestTrackState.hpp"
 #include "Acts/Utilities/HashedString.hpp"
 #include "Acts/Utilities/Holders.hpp"
 #include "Acts/Utilities/Zip.hpp"
@@ -45,7 +45,8 @@ using namespace Acts::UnitLiterals;
 
 using namespace Acts;
 using namespace Acts::HashedStringLiteral;
-using namespace Acts::Test;
+using namespace Acts::detail::Test;
+
 using MultiTrajectoryTraits::IndexType;
 namespace bd = boost::unit_test::data;
 
diff --git a/Tests/UnitTests/Core/Seeding/EstimateTrackParamsFromSeedTest.cpp b/Tests/UnitTests/Core/Seeding/EstimateTrackParamsFromSeedTest.cpp
index 114000066ec..632cb9b6c46 100644
--- a/Tests/UnitTests/Core/Seeding/EstimateTrackParamsFromSeedTest.cpp
+++ b/Tests/UnitTests/Core/Seeding/EstimateTrackParamsFromSeedTest.cpp
@@ -14,6 +14,7 @@
 #include "Acts/Definitions/Units.hpp"
 #include "Acts/EventData/GenericCurvilinearTrackParameters.hpp"
 #include "Acts/EventData/TrackParameters.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Geometry/GeometryIdentifier.hpp"
 #include "Acts/Geometry/LayerCreator.hpp"
@@ -28,7 +29,7 @@
 #include "Acts/Tests/CommonHelpers/CylindricalTrackingGeometry.hpp"
 #include "Acts/Tests/CommonHelpers/FloatComparisons.hpp"
 #include "Acts/Tests/CommonHelpers/MeasurementsCreator.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
+#include "Acts/Utilities/CalibrationContext.hpp"
 #include "Acts/Utilities/Logger.hpp"
 
 #include <algorithm>
diff --git a/Tests/UnitTests/Core/SpacePointFormation/SpacePointBuilderTests.cpp b/Tests/UnitTests/Core/SpacePointFormation/SpacePointBuilderTests.cpp
index 5995a3467e3..5dee017ed2e 100644
--- a/Tests/UnitTests/Core/SpacePointFormation/SpacePointBuilderTests.cpp
+++ b/Tests/UnitTests/Core/SpacePointFormation/SpacePointBuilderTests.cpp
@@ -17,6 +17,7 @@
 #include "Acts/EventData/Measurement.hpp"
 #include "Acts/EventData/SourceLink.hpp"
 #include "Acts/EventData/TrackParameters.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Geometry/GeometryIdentifier.hpp"
 #include "Acts/Geometry/TrackingGeometry.hpp"
@@ -32,7 +33,6 @@
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Tests/CommonHelpers/CubicTrackingGeometry.hpp"
 #include "Acts/Tests/CommonHelpers/MeasurementsCreator.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
 #include "Acts/Tests/CommonHelpers/TestSpacePoint.hpp"
 
 #include <algorithm>
@@ -53,7 +53,7 @@ namespace Test {
 using namespace UnitLiterals;
 
 using StraightPropagator = Propagator<StraightLineStepper, Navigator>;
-
+using TestSourceLink = detail::Test::TestSourceLink;
 using ConstantFieldStepper = EigenStepper<>;
 using ConstantFieldPropagator = Propagator<ConstantFieldStepper, Navigator>;
 // Construct initial track parameters.
diff --git a/Tests/UnitTests/Core/TrackFinding/CombinatorialKalmanFilterTests.cpp b/Tests/UnitTests/Core/TrackFinding/CombinatorialKalmanFilterTests.cpp
index d7e6568699d..0bb9e67e4bf 100644
--- a/Tests/UnitTests/Core/TrackFinding/CombinatorialKalmanFilterTests.cpp
+++ b/Tests/UnitTests/Core/TrackFinding/CombinatorialKalmanFilterTests.cpp
@@ -22,6 +22,7 @@
 #include "Acts/EventData/TrackStatePropMask.hpp"
 #include "Acts/EventData/VectorMultiTrajectory.hpp"
 #include "Acts/EventData/VectorTrackContainer.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Geometry/GeometryIdentifier.hpp"
 #include "Acts/MagneticField/ConstantBField.hpp"
@@ -35,7 +36,6 @@
 #include "Acts/Tests/CommonHelpers/CubicTrackingGeometry.hpp"
 #include "Acts/Tests/CommonHelpers/LineSurfaceStub.hpp"
 #include "Acts/Tests/CommonHelpers/MeasurementsCreator.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
 #include "Acts/TrackFinding/CombinatorialKalmanFilter.hpp"
 #include "Acts/TrackFinding/MeasurementSelector.hpp"
 #include "Acts/TrackFitting/GainMatrixSmoother.hpp"
@@ -71,6 +71,7 @@ class TrackingGeometry;
 namespace {
 
 using namespace Acts::Test;
+using namespace Acts::detail::Test;
 using namespace Acts::UnitLiterals;
 
 static const auto pion = Acts::ParticleHypothesis::pion();
diff --git a/Tests/UnitTests/Core/TrackFitting/FitterTestsCommon.hpp b/Tests/UnitTests/Core/TrackFitting/FitterTestsCommon.hpp
index 0ee51ca526c..4e17b47b82e 100644
--- a/Tests/UnitTests/Core/TrackFitting/FitterTestsCommon.hpp
+++ b/Tests/UnitTests/Core/TrackFitting/FitterTestsCommon.hpp
@@ -15,6 +15,7 @@
 #include "Acts/EventData/SourceLink.hpp"
 #include "Acts/EventData/VectorMultiTrajectory.hpp"
 #include "Acts/EventData/VectorTrackContainer.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Geometry/TrackingGeometry.hpp"
 #include "Acts/MagneticField/ConstantBField.hpp"
 #include "Acts/MagneticField/MagneticFieldContext.hpp"
@@ -23,7 +24,6 @@
 #include "Acts/Tests/CommonHelpers/CubicTrackingGeometry.hpp"
 #include "Acts/Tests/CommonHelpers/FloatComparisons.hpp"
 #include "Acts/Tests/CommonHelpers/MeasurementsCreator.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
 #include "Acts/TrackFitting/detail/KalmanGlobalCovariance.hpp"
 #include "Acts/Utilities/CalibrationContext.hpp"
 #include "Acts/Utilities/Logger.hpp"
@@ -125,7 +125,8 @@ struct FitterTester {
   CubicTrackingGeometry geometryStore{geoCtx};
   std::shared_ptr<const Acts::TrackingGeometry> geometry = geometryStore();
 
-  TestSourceLink::SurfaceAccessor surfaceAccessor{*geometry};
+  Acts::detail::Test::TestSourceLink::SurfaceAccessor surfaceAccessor{
+      *geometry};
 
   // expected number of measurements for the given detector
   constexpr static std::size_t nMeasurements = 6u;
@@ -147,7 +148,7 @@ struct FitterTester {
       makeStraightPropagator(geometry);
 
   static std::vector<Acts::SourceLink> prepareSourceLinks(
-      const std::vector<TestSourceLink>& sourceLinks) {
+      const std::vector<Acts::detail::Test::TestSourceLink>& sourceLinks) {
     std::vector<Acts::SourceLink> result;
     std::transform(sourceLinks.begin(), sourceLinks.end(),
                    std::back_inserter(result),
diff --git a/Tests/UnitTests/Core/TrackFitting/GainMatrixUpdaterTests.cpp b/Tests/UnitTests/Core/TrackFitting/GainMatrixUpdaterTests.cpp
index d919c1f828d..1e103d0c5e9 100644
--- a/Tests/UnitTests/Core/TrackFitting/GainMatrixUpdaterTests.cpp
+++ b/Tests/UnitTests/Core/TrackFitting/GainMatrixUpdaterTests.cpp
@@ -14,9 +14,9 @@
 #include "Acts/EventData/SourceLink.hpp"
 #include "Acts/EventData/TrackStatePropMask.hpp"
 #include "Acts/EventData/VectorMultiTrajectory.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Tests/CommonHelpers/FloatComparisons.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
 #include "Acts/TrackFitting/GainMatrixUpdater.hpp"
 #include "Acts/Utilities/CalibrationContext.hpp"
 #include "Acts/Utilities/Result.hpp"
@@ -29,6 +29,7 @@ namespace {
 
 using namespace Acts;
 using namespace Acts::Test;
+using namespace Acts::detail::Test;
 
 using ParametersVector = Acts::BoundVector;
 using CovarianceMatrix = Acts::BoundSquareMatrix;
diff --git a/Tests/UnitTests/Core/TrackFitting/GsfTests.cpp b/Tests/UnitTests/Core/TrackFitting/GsfTests.cpp
index 636d2c2bc54..8a3611bda61 100644
--- a/Tests/UnitTests/Core/TrackFitting/GsfTests.cpp
+++ b/Tests/UnitTests/Core/TrackFitting/GsfTests.cpp
@@ -24,6 +24,7 @@
 #include "Acts/EventData/TrackStatePropMask.hpp"
 #include "Acts/EventData/VectorMultiTrajectory.hpp"
 #include "Acts/EventData/VectorTrackContainer.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/EventData/detail/TransformationFreeToBound.hpp"
 #include "Acts/Geometry/GeometryIdentifier.hpp"
 #include "Acts/Propagator/MultiEigenStepperLoop.hpp"
@@ -34,7 +35,6 @@
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Tests/CommonHelpers/LineSurfaceStub.hpp"
 #include "Acts/Tests/CommonHelpers/MeasurementsCreator.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
 #include "Acts/TrackFitting/BetheHeitlerApprox.hpp"
 #include "Acts/TrackFitting/GainMatrixUpdater.hpp"
 #include "Acts/TrackFitting/GaussianSumFitter.hpp"
@@ -64,6 +64,7 @@ namespace {
 
 using namespace Acts;
 using namespace Acts::Test;
+using namespace Acts::detail::Test;
 using namespace Acts::UnitLiterals;
 
 static const auto electron = ParticleHypothesis::electron();
diff --git a/Tests/UnitTests/Core/TrackFitting/Gx2fTests.cpp b/Tests/UnitTests/Core/TrackFitting/Gx2fTests.cpp
index 7fc71e3b32d..30ba23d6e4c 100644
--- a/Tests/UnitTests/Core/TrackFitting/Gx2fTests.cpp
+++ b/Tests/UnitTests/Core/TrackFitting/Gx2fTests.cpp
@@ -12,6 +12,7 @@
 #include "Acts/Definitions/Units.hpp"
 #include "Acts/EventData/VectorMultiTrajectory.hpp"
 #include "Acts/EventData/VectorTrackContainer.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Geometry/CuboidVolumeBuilder.hpp"
 #include "Acts/Geometry/Layer.hpp"
 #include "Acts/Geometry/TrackingGeometry.hpp"
@@ -28,7 +29,6 @@
 #include "Acts/Tests/CommonHelpers/DetectorElementStub.hpp"
 #include "Acts/Tests/CommonHelpers/MeasurementsCreator.hpp"
 #include "Acts/Tests/CommonHelpers/PredefinedMaterials.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
 #include "Acts/TrackFitting/GlobalChiSquareFitter.hpp"
 #include "Acts/Utilities/Logger.hpp"
 
@@ -37,6 +37,7 @@
 #include "FitterTestsCommon.hpp"
 
 using namespace Acts::UnitLiterals;
+using namespace Acts::detail::Test;
 
 Acts::Logging::Level logLevel = Acts::Logging::VERBOSE;
 const auto gx2fLogger = Acts::getDefaultLogger("Gx2f", logLevel);
diff --git a/Tests/UnitTests/Core/TrackFitting/KalmanFitterTests.cpp b/Tests/UnitTests/Core/TrackFitting/KalmanFitterTests.cpp
index 38247a6cab4..710579ca73c 100644
--- a/Tests/UnitTests/Core/TrackFitting/KalmanFitterTests.cpp
+++ b/Tests/UnitTests/Core/TrackFitting/KalmanFitterTests.cpp
@@ -17,12 +17,12 @@
 #include "Acts/EventData/TrackParameters.hpp"
 #include "Acts/EventData/TrackStatePropMask.hpp"
 #include "Acts/EventData/VectorMultiTrajectory.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Propagator/EigenStepper.hpp"
 #include "Acts/Propagator/Navigator.hpp"
 #include "Acts/Propagator/Propagator.hpp"
 #include "Acts/Propagator/StraightLineStepper.hpp"
 #include "Acts/Tests/CommonHelpers/LineSurfaceStub.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
 #include "Acts/TrackFitting/GainMatrixSmoother.hpp"
 #include "Acts/TrackFitting/GainMatrixUpdater.hpp"
 #include "Acts/TrackFitting/KalmanFitter.hpp"
@@ -43,6 +43,7 @@ namespace {
 
 using namespace Acts;
 using namespace Acts::Test;
+using namespace Acts::detail::Test;
 using namespace Acts::UnitLiterals;
 
 using StraightPropagator =
@@ -97,9 +98,9 @@ auto makeDefaultKalmanFitterOptions() {
       &kfUpdater);
   extensions.smoother
       .connect<&KalmanSmoother::operator()<VectorMultiTrajectory>>(&kfSmoother);
-  extensions.surfaceAccessor
-      .connect<&Acts::Test::TestSourceLink::SurfaceAccessor::operator()>(
-          &tester.surfaceAccessor);
+  extensions.surfaceAccessor.connect<
+      &Acts::detail::Test::TestSourceLink::SurfaceAccessor::operator()>(
+      &tester.surfaceAccessor);
 
   return KalmanFitterOptions(tester.geoCtx, tester.magCtx, tester.calCtx,
                              extensions, PropagatorPlainOptions());
diff --git a/Tests/UnitTests/Core/Visualization/EventDataView3DBase.hpp b/Tests/UnitTests/Core/Visualization/EventDataView3DBase.hpp
index 1f70d465db9..5c103322625 100644
--- a/Tests/UnitTests/Core/Visualization/EventDataView3DBase.hpp
+++ b/Tests/UnitTests/Core/Visualization/EventDataView3DBase.hpp
@@ -15,6 +15,7 @@
 #include "Acts/EventData/TrackParameters.hpp"
 #include "Acts/EventData/VectorMultiTrajectory.hpp"
 #include "Acts/EventData/VectorTrackContainer.hpp"
+#include "Acts/EventData/detail/TestSourceLink.hpp"
 #include "Acts/Geometry/CuboidVolumeBuilder.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Geometry/TrackingGeometry.hpp"
@@ -30,7 +31,6 @@
 #include "Acts/Surfaces/RectangleBounds.hpp"
 #include "Acts/Tests/CommonHelpers/DetectorElementStub.hpp"
 #include "Acts/Tests/CommonHelpers/PredefinedMaterials.hpp"
-#include "Acts/Tests/CommonHelpers/TestSourceLink.hpp"
 #include "Acts/TrackFitting/GainMatrixSmoother.hpp"
 #include "Acts/TrackFitting/GainMatrixUpdater.hpp"
 #include "Acts/TrackFitting/KalmanFitter.hpp"
@@ -232,7 +232,7 @@ static inline std::string testMeasurement(IVisualization3D& helper) {
   // Create measurements (assuming they are for a linear track parallel to
   // global x-axis)
   std::cout << "Creating measurements:" << std::endl;
-  std::vector<Test::TestSourceLink> sourcelinks;
+  std::vector<detail::Test::TestSourceLink> sourcelinks;
   sourcelinks.reserve(nSurfaces);
   Vector2 lPosCenter{5_mm, 5_mm};
   Vector2 resolution{200_um, 150_um};
@@ -242,7 +242,7 @@ static inline std::string testMeasurement(IVisualization3D& helper) {
     Vector2 loc = lPosCenter;
     loc[0] += resolution[0] * gauss(generator);
     loc[1] += resolution[1] * gauss(generator);
-    sourcelinks.emplace_back(Test::TestSourceLink{
+    sourcelinks.emplace_back(detail::Test::TestSourceLink{
         eBoundLoc0, eBoundLoc1, loc, cov2D, surface->geometryId()});
   }
 
@@ -303,7 +303,7 @@ static inline std::string testMultiTrajectory(IVisualization3D& helper) {
     Vector2 loc = lPosCenter;
     loc[0] += resolution[0] * gauss(generator);
     loc[1] += resolution[1] * gauss(generator);
-    sourcelinks.emplace_back(Test::TestSourceLink{
+    sourcelinks.emplace_back(detail::Test::TestSourceLink{
         eBoundLoc0, eBoundLoc1, loc, cov2D, surface->geometryId()});
   }
 
@@ -344,8 +344,8 @@ static inline std::string testMultiTrajectory(IVisualization3D& helper) {
   Acts::GainMatrixSmoother kfSmoother;
 
   KalmanFitterExtensions<VectorMultiTrajectory> extensions;
-  extensions.calibrator
-      .connect<&Test::testSourceLinkCalibrator<VectorMultiTrajectory>>();
+  extensions.calibrator.connect<
+      &detail::Test::testSourceLinkCalibrator<VectorMultiTrajectory>>();
   extensions.updater
       .connect<&Acts::GainMatrixUpdater::operator()<VectorMultiTrajectory>>(
           &kfUpdater);
@@ -353,9 +353,9 @@ static inline std::string testMultiTrajectory(IVisualization3D& helper) {
       .connect<&Acts::GainMatrixSmoother::operator()<VectorMultiTrajectory>>(
           &kfSmoother);
 
-  Test::TestSourceLink::SurfaceAccessor surfaceAccessor{*detector};
+  detail::Test::TestSourceLink::SurfaceAccessor surfaceAccessor{*detector};
   extensions.surfaceAccessor
-      .connect<&Test::TestSourceLink::SurfaceAccessor::operator()>(
+      .connect<&detail::Test::TestSourceLink::SurfaceAccessor::operator()>(
           &surfaceAccessor);
 
   KalmanFitterOptions kfOptions(tgContext, mfContext, calContext, extensions,
diff --git a/Tests/UnitTests/Fatras/Digitization/UncorrelatedHitSmearerTests.cpp b/Tests/UnitTests/Fatras/Digitization/UncorrelatedHitSmearerTests.cpp
index f09e82faaab..9e1b71ff483 100644
--- a/Tests/UnitTests/Fatras/Digitization/UncorrelatedHitSmearerTests.cpp
+++ b/Tests/UnitTests/Fatras/Digitization/UncorrelatedHitSmearerTests.cpp
@@ -13,13 +13,13 @@
 #include "Acts/Definitions/Common.hpp"
 #include "Acts/Definitions/TrackParametrization.hpp"
 #include "Acts/Definitions/Units.hpp"
+#include "Acts/EventData/detail/GenerateParameters.hpp"
 #include "Acts/EventData/detail/TransformationBoundToFree.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Geometry/GeometryIdentifier.hpp"
 #include "Acts/Surfaces/PlaneSurface.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Tests/CommonHelpers/FloatComparisons.hpp"
-#include "Acts/Tests/CommonHelpers/GenerateParameters.hpp"
 #include "Acts/Utilities/Result.hpp"
 #include "ActsFatras/Digitization/DigitizationError.hpp"
 #include "ActsFatras/Digitization/UncorrelatedHitSmearer.hpp"
@@ -96,7 +96,8 @@ struct Fixture {
     surface->assignGeometryId(gid);
 
     // generate random track parameters
-    auto [par, cov] = Acts::Test::generateBoundParametersCovariance(rng);
+    auto [par, cov] =
+        Acts::detail::Test::generateBoundParametersCovariance(rng);
     boundParams = par;
     freeParams = Acts::detail::transformBoundToFreeParameters(*surface, geoCtx,
                                                               boundParams);
diff --git a/Tests/UnitTests/Plugins/Podio/PodioTrackStateContainerTest.cpp b/Tests/UnitTests/Plugins/Podio/PodioTrackStateContainerTest.cpp
index 929d3661494..24bc17ac78f 100644
--- a/Tests/UnitTests/Plugins/Podio/PodioTrackStateContainerTest.cpp
+++ b/Tests/UnitTests/Plugins/Podio/PodioTrackStateContainerTest.cpp
@@ -15,11 +15,11 @@
 #include "Acts/Definitions/Units.hpp"
 #include "Acts/EventData/SourceLink.hpp"
 #include "Acts/EventData/TrackStatePropMask.hpp"
+#include "Acts/EventData/detail/MultiTrajectoryTestsCommon.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Plugins/Podio/PodioTrackStateContainer.hpp"
 #include "Acts/Plugins/Podio/PodioUtil.hpp"
 #include "Acts/Surfaces/RectangleBounds.hpp"
-#include "Acts/Tests/CommonHelpers/MultiTrajectoryTestsCommon.hpp"
 #include "ActsPodioEdm/BoundParametersCollection.h"
 #include "ActsPodioEdm/JacobianCollection.h"
 #include "ActsPodioEdm/TrackStateCollection.h"
@@ -34,7 +34,7 @@ namespace {
 
 using namespace Acts;
 using namespace Acts::UnitLiterals;
-using namespace Acts::Test;
+using namespace Acts::detail::Test;
 namespace bd = boost::unit_test::data;
 
 std::default_random_engine rng(31415);