Understanding TOTW 153 example with namespace polution - c++

Question

In TOTW 153 it is claimed that using namespace in function scope can leak in the global scope,
in other words they claim this is:
namespace totw {
namespace example {
namespace {
TEST(MyTest, UsesUsingDirectives) {
using namespace ::testing;
Sequence seq; // ::testing::Sequence
WallTimer timer; // ::WallTimer
}
} // namespace
} // namespace example
} // namespace totw
roughly equivalent to:
using ::testing::Expectation;
using ::testing::Sequence;
using ::testing::UnorderedElementsAre;
...
// many, many more symbols are injected into the global namespace
namespace totw {
namespace example {
namespace {
TEST(MyTest, UsesUsingDirectives) {
Sequence seq; // ::testing::Sequence
WallTimer timer; // ::WallTimer
...
}
} // namespace
} // namespace example
} // namespace totw
So I expected that if I do this it will compile:
#include <gtest/gtest.h>
#include <gmock/gmock.h>
namespace totw {
namespace example {
namespace {
TEST(MyTest, UsesUsingDirectives) {
using namespace ::testing;
Sequence seq; // ::testing::Sequence
}
} // namespace
} // namespace example
} // namespace totw
Sequence s; //notice no testing::
It does not. So I wonder if I am wrong in replicating the example, or is the TOTW153 example misleading?
My best guess is that their example is "wrong" in a sense that what they claim is roughly equivalent is not really equivalent in a sense I would assume it is.

Answer 1

You are correct that the "transpiled" code could lead one to think that your last snippet should work. But that's not what they meant.
The using ::testing::Expectation etc. are added to the global namespace from the perspective of the TEST scope. In other words, the transpiled code is effectively identical to the original only within the TEST scope. Outside of that scope there is no effect, but the problems they list are still problems (unless you know that neither the TEST scope contents nor the contents of any involved namespaces will ever be changed). In other words, the using introduces potential collisions between all (present and future) symbols in that TEST scope and the symbols (present and future) in all the involved namespaces. Sounds less scary but will still bite you in the long run.