Namespaces qualified with :: in C++

Question

What does it mean if namespace in C++ is qualified with ::? For example ::testing::Test.

Answer 1

This invokes something called the qualified name lookup:

$3.4.3/1 - "The name of a class or namespace member can be referred to after the :: scope resolution operator (5.1) applied to a nested-name-specifier that nominates its class or namespace. During the lookup for a name preceding the :: scope resolution operator, object, function, and enumerator names are ignored. If the name found is not a class-name (clause 9) or namespace-name (7.3.1), the program is ill-formed."