This test can be carried out to check that the chimney flue is sound. (Sometimes called a soundness test)
The flue is sealed at both ends ( the opening of the fireplace is covered and sealed and the top is bunged) smoke is then released into the flue causing a pressure build up and numerous checks are carried out to insure that the smoke does not release within the property.
Building regulation certificate are issued with this test. A stove can be installed if the flue passes the test without a liner. However some stoves do still require a liner for efficiency and all stoves will not be as efficient without one.