Catch requires test files to be compulation units.

test/CMakeLists.txt

@@ -1,3 +1,13 @@
 include_directories(../lib)
 
-add_executable (test_bin test_main.cpp)
+add_executable (
+test_bin
+
+graph/test_graph.cpp
+graph/test_priority_queue.cpp
+graph/test_quad_tree.cpp
+graph/test_graph_algorithms.cpp
+
+test_main.cpp)
+
+target_link_libraries(test_bin gcov)

test/test_main.cpp

@@ -1,5 +1,2 @@
 #define CATCH_CONFIG_MAIN
 #include "catch.hpp"
-
-#include "graph/test_graph.hpp"
-#include "graph/test_graph_algorithms.hpp"