Black Box Testing

Strictly speaking, black box testing involves testing a system as a whole, not as a
system of connected parts. Realistically, however, black box testing still provides some differentiation between clients, the server, and the network connecting them. This
means that when performing black box testing, it is possible to determine whether time
is being spent in the client, the network, or the server, and hence determine where
bottlenecks lie.

The limitation of this approach is that knowing, for example, that the server is the
bottleneck of a system is not necessarily sufficient. Is the bottleneck caused by a lack of memory, a lack of CPU performance, poor algorithms, or one of many other causes? To answer these questions, diagnostics need to be performed on the server while
generating a load.