Revert "Remove CTestTestfile.cmake when BUILD_TESTING is OFF"

Revert commit v3.8.0-rc1~305^2 (Remove CTestTestfile.cmake when BUILD_TESTING
is OFF, 2016-11-14) again.  We reverted it once in commit v3.8.0-rc3~22^2
(Revert "Remove CTestTestfile.cmake when BUILD_TESTING is OFF", 2017-03-06) but
it was accidentally restored by commit v3.11.0-rc1~387^2 (server: add
"ctestInfo" request to get test info, 2017-10-25), perhaps due to conflict
resolution during rebase.

We cannot remove `CTestTestfile.cmake` when testing is off because it breaks
projects that never enable testing but create their own `CTestTestfile.cmake`
manually instead.  Revert the change again and add a test case.

1 files changed, 4 insertions, 7 deletions

diff --git a/Source/cmLocalGenerator.cxx b/Source/cmLocalGenerator.cxx
index cee540b..e942ff4 100644
--- a/Source/cmLocalGenerator.cxx
+++ b/Source/cmLocalGenerator.cxx
@@ -224,14 +224,7 @@ void cmLocalGenerator::TraceDependencies()
 
 void cmLocalGenerator::GenerateTestFiles()
 {
-  std::string file = this->StateSnapshot.GetDirectory().GetCurrentBinary();
-  file += "/";
-  file += "CTestTestfile.cmake";
-
   if (!this->Makefile->IsOn("CMAKE_TESTING_ENABLED")) {
-    if (cmSystemTools::FileExists(file)) {
-      cmSystemTools::RemoveFile(file);
-    }
     return;
   }
 
@@ -240,6 +233,10 @@ void cmLocalGenerator::GenerateTestFiles()
   const std::string& config =
     this->Makefile->GetConfigurations(configurationTypes, false);
 
+  std::string file = this->StateSnapshot.GetDirectory().GetCurrentBinary();
+  file += "/";
+  file += "CTestTestfile.cmake";
+
   cmGeneratedFileStream fout(file.c_str());
   fout.SetCopyIfDifferent(true);