diff --git a/CMakeLists.txt b/CMakeLists.txt
index e66cf10..c5ce1f9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -73,10 +73,11 @@ target_sources(vissim PRIVATE
 # Tests
 add_executable(runtests)
 
-target_sources(runtests PRIVATE tests/runtests.cc tests/CollisionTests.cc)
+target_sources(runtests PRIVATE tests/runtests.cc tests/CollisionTests.cc src/utils.cc)
 target_include_directories(
 		runtests
 		PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+		PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
 		PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/3rdparty/rbdl/include>
 		PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/3rdparty/rbdl/include>)
 
diff --git a/include/rbdlsim.h b/include/rbdlsim.h
index bbbd1d8..3e32bd9 100644
--- a/include/rbdlsim.h
+++ b/include/rbdlsim.h
@@ -96,6 +96,7 @@ bool CheckPenetrationSphereVsPlane(
 SimBody CreateSphereBody(
     double mass,
     double radius,
+    double restitution,
     const Vector3d& pos,
     const Vector3d& vel);
 
@@ -110,8 +111,8 @@ void PrepareConstraintImpulse(
     SimBody* body_b,
     CollisionInfo& cinfo);
 void CalcCollisions(
-    const SimBody& body_a,
-    const SimBody& body_b,
+    SimBody& body_a,
+    SimBody& body_b,
     std::vector<CollisionInfo>& collisions);
 void CalcConstraintImpulse(
     SimBody* body_a,
diff --git a/src/utils.cc b/src/utils.cc
index 4ab7d6c..7c0dc7b 100644
--- a/src/utils.cc
+++ b/src/utils.cc
@@ -4,8 +4,21 @@
 #include <cstdlib>
 #include <fstream>
 
+static Timer sTimer;
+Timer* gTimer = &sTimer;
+double gTimeAtStart = 0;
+
 FILE* gLogFile = NULL;
 
+void gTimerInit() {
+  sTimer.mCurrentTime = 0.;
+  sTimer.mDeltaTime = 0.;
+  sTimer.mFrameTime = 0.;
+  sTimer.mPaused = false;
+
+  gTimeAtStart = gGetCurrentTime();
+}
+
 void GuiInputState_Init(GuiInputState* input_state) {
   input_state->mouseX = 0;
   input_state->mouseY = 0;
diff --git a/src/utils.h b/src/utils.h
index a438fc9..af01bc9 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -40,6 +40,16 @@ inline void gGetFileModTime(const char* filename, int* sec, int* nsec) {
   *nsec = attr.st_mtim.tv_nsec;
 }
 
+typedef struct Timer {
+  float mCurrentTime;
+  float mFrameTime;
+  float mDeltaTime;
+  bool mPaused;
+}Timer;
+
+extern Timer* gTimer;
+void gTimerInit();
+
 inline double gGetCurrentTime() {
   struct timespec spec;
   clock_gettime(CLOCK_REALTIME, &spec);
diff --git a/src/vissim.cc b/src/vissim.cc
index a0a4d9c..f1663f0 100644
--- a/src/vissim.cc
+++ b/src/vissim.cc
@@ -21,17 +21,8 @@
 #include "srender.h"
 #include "simulator.h"
 
-struct Timer {
-  float mCurrentTime = 0.0f;
-  float mFrameTime = 0.0f;
-  float mDeltaTime = 0.0f;
-  bool mPaused = false;
-};
-
-Timer* gTimer = nullptr;
 GLFWwindow* gWindow = nullptr;
 GuiInputState* gGuiInputState = nullptr;
-double gTimeAtStart = 0;
 
 // Rendering
 srndr* gRndr = nullptr;
@@ -41,8 +32,6 @@ srcmdbuf* gRndrCmds = nullptr;
 double mouse_scroll_x = 0.;
 double mouse_scroll_y = 0.;
 
-static Timer sTimer;
-
 using namespace std;
 
 static void error_callback(int error, const char* description) {
@@ -215,10 +204,7 @@ void DoRender() {
 }
 
 int main(void) {
-  gTimeAtStart = gGetCurrentTime();
-  std::cout << "Time at start: " << gTimeAtStart << std::endl;
-
-  gTimer = &sTimer;
+  gTimerInit();
 
   LoggingInit();
 
diff --git a/tests/runtests.cc b/tests/runtests.cc
index 48f1283..02399fd 100644
--- a/tests/runtests.cc
+++ b/tests/runtests.cc
@@ -1,2 +1,12 @@
-#define CATCH_CONFIG_MAIN  // This tells Catch to provide a main() - only do this in one cpp file
-#include "catch.hpp"
\ No newline at end of file
+#define CATCH_CONFIG_RUNNER  // This tells Catch to provide a main() - only do this in one cpp file
+#include "catch.hpp"
+
+#include "utils.h"
+
+int main (int argc, char* argv[]) {
+  LoggingInit();
+
+  int result = Catch::Session().run(argc, argv);
+
+  return result;
+}
\ No newline at end of file