Inserting a brass rod in the test tube will not increase the strength of the magnetic field of the solenoid. The strength of the magnetic field inside a solenoid depends on factors such as the number of turns of wire, the current passing through it, and the core material within the solenoid. Materials with high permeability, like soft iron and steel, can enhance the strength of the magnetic field when inserted into the solenoid. Nickel, which also has some ferromagnetic properties, would have a similar effect. However, brass is not a ferromagnetic material; it does not enhance the magnetic field strength when inserted into the solenoid. In fact, it might even slightly reduce the magnetic field strength due to its non-magnetic properties.