project(): Add tests verifying variables set by second project() call

Tests/RunCMake/project/ProjectTwice.cmake

@@ -0,0 +1,26 @@
+cmake_policy(SET CMP0048 NEW)
+project(ProjectTwiceTestFirst
+  VERSION 1.2.3.4
+  DESCRIPTION "Test Project"
+  HOMEPAGE_URL "http://example.com"
+  LANGUAGES NONE
+)
+
+project(ProjectTwiceTestSecond LANGUAGES NONE)
+
+foreach(var
+  PROJECT_VERSION
+  PROJECT_VERSION_MAJOR
+  PROJECT_VERSION_MINOR
+  PROJECT_VERSION_PATCH
+  PROJECT_VERSION_TWEAK
+  PROJECT_DESCRIPTION
+  PROJECT_HOMEPAGE_URL
+)
+  if(${var})
+    message(SEND_ERROR "${var} set but should be empty")
+  endif()
+  if(CMAKE_${var})
+    message(SEND_ERROR "CMAKE_${var} set but should be empty")
+  endif()
+endforeach()

Tests/RunCMake/project/RunCMakeTest.cmake

@@ -15,6 +15,7 @@ run_cmake(ProjectDescriptionNoArg2)
 run_cmake(ProjectHomepage)
 run_cmake(ProjectHomepage2)
 run_cmake(ProjectHomepageNoArg)
+run_cmake(ProjectTwice)
 run_cmake(VersionAndLanguagesEmpty)
 run_cmake(VersionEmpty)
 run_cmake(VersionInvalid)