Add a simple post-install test.

To test that ROOT is usable after it has been installed, a small CMake
project is added that checks the outputs of hsimple.

Author: hageboeck

test/PostInstall/CMakeLists.txt

@@ -0,0 +1,21 @@
+cmake_minimum_required(VERSION 3.20 FATAL_ERROR)
+
+project(PostInstall)
+
+find_package(ROOT REQUIRED)
+
+add_executable(readHSimple readHSimple.cxx)
+target_link_libraries(readHSimple PUBLIC ROOT::Hist ROOT::RIO)
+
+include(CTest)
+
+if(BUILD_TESTING)
+  add_test(NAME run-hsimple
+    COMMAND ${ROOT_BINDIR}/root.exe -b -q -l -e ".x ${CMAKE_SOURCE_DIR}/../../tutorials/hsimple.C" -e "return"
+    WORKING_DIRECTORY ${CMAKE_BINARY_DIR})
+  add_test(NAME read-hsimple
+    COMMAND $<TARGET_FILE:readHSimple>
+    WORKING_DIRECTORY ${CMAKE_BINARY_DIR})
+  set_tests_properties(run-hsimple   PROPERTIES FIXTURES_SETUP    HSIMPLE)
+  set_tests_properties(read-hsimple  PROPERTIES FIXTURES_REQUIRED HSIMPLE)
+endif()

test/PostInstall/readHSimple.cxx

@@ -0,0 +1,15 @@
+#include <TH1.h>
+#include <TFile.h>
+
+int main() {
+  TFile file("hsimple.root", "READ");
+  if (!file.IsOpen()) return 1;
+
+  TH1 * histo = file.Get<TH1>("hpx");
+  if (!histo) return 2;
+
+  if (histo->GetEntries() != 25000) return 3;
+  histo->Print();
+
+  return 0;
+}