addressing comments

tests/notnull_tests.cpp

@@ -27,12 +27,13 @@
 //disable warnings from gtest
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wundef"
-#endif
+#endif // __clang__ || __GNUC__
+
 #if __clang__
 #pragma GCC diagnostic ignored "-Wglobal-constructors"
 #pragma GCC diagnostic ignored "-Wused-but-marked-unused"
 #pragma GCC diagnostic ignored "-Wcovered-switch-default"
-#endif
+#endif // __clang__
 
 #include <gtest/gtest.h>
 
@@ -52,9 +53,9 @@ struct fail_fast;
 
 using namespace gsl;
 
-namespace{
-static const char *deathstring("Expected Death");
-}
+namespace
+{
+static constexpr char deathstring[] = "Expected Death";
 
 struct MyBase
 {
@@ -148,7 +149,7 @@ GSL_SUPPRESS(f.4) // NO-FORMAT: attribute
 bool helper_const(not_null<const int*> p) { return *p == 12; }
 
 int* return_pointer() { return nullptr; }
-const int* return_pointer_const() { return nullptr; }
+} //namespace
 
 TEST(notnull_tests, TestNotNullConstructors)
 {
@@ -564,4 +565,4 @@ static_assert(std::is_nothrow_move_constructible<not_null<void*>>::value,
 
 #if __clang__ || __GNUC__
 #pragma GCC diagnostic pop
-#endif
+#endif // __clang__ || __GNUC__