build: fetch doctest during configuration

test/CMakeLists.txt

@@ -1,5 +1,15 @@
-add_library(doctest INTERFACE)
-target_include_directories(doctest INTERFACE doctest)
+include(FetchContent)
+
+FetchContent_Declare(
+    DocTest
+    GIT_REPOSITORY https://github.com/doctest/doctest.git
+    GIT_TAG v2.4.9
+)
+
+FetchContent_MakeAvailable(DocTest)
+
+#add_library(doctest INTERFACE)
+#target_include_directories(doctest INTERFACE doctest)
 
 add_executable(test setup.cpp testBoundaryCondition.cpp testDiffusion.cpp)
 target_link_libraries(test doctest BTCSDiffusion)

test/setup.cpp

@@ -1,2 +1,2 @@
 #define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
-#include "doctest.h"
+#include <doctest/doctest.h>

test/testBoundaryCondition.cpp

@@ -1,5 +1,5 @@
 #include <grid/BTCSBoundaryCondition.hpp>
-#include <doctest.h>
+#include <doctest/doctest.h>
 
 using namespace Diffusion;
 

test/testDiffusion.cpp

@@ -1,7 +1,7 @@
 #include <bits/stdint-uintn.h>
 #include <grid/BTCSBoundaryCondition.hpp>
 #include <diffusion/BTCSDiffusion.hpp>
-#include <doctest.h>
+#include <doctest/doctest.h>
 #include <vector>
 
 using namespace Diffusion;