Simple Test Equipment.

If you are thinking of buying a radio that has been converted to 4m you will only need very basic equipment to check out the transmit power:

The Bird Wattmeter is an excellent meter for doing this, but you will have to ensure that you have the correct inserts for the 4m band. The meter and the inserts can be a bit pricy but there is always a cheaper way to go..

Bird Wattmeter

Various Inserts For Bird Wattmeter

There is also a Power Meter such as the HP one shown here, again this can be pricy and if you want to keep things simple then a good SWR/Power meter will suffice, see the Watson W-220 and the Comet CD-120.

HP 432A Power Meter

The only thing about getting an SWR/Power meter is to ensure that they cover the frequency range and power  that you want to test. Along with the SWR/power meter you will need to get a good Dummy load, also ensuring that they cover the frequency range and power you want to test.

Watson W-220 1.6Mhz to 200Mhz  200Watts

Comet CD-120 1.8Mhz to 200Mhz  200Watts

My rule of thumb is that if you are looking to test a 25w radio then buy a 50w dummy load.

You can always just use a tuned, low SWR antenna with your SWR/Power meter to check the output power but I always find that the Dummy Load gives a more accurate power reading.

Various Dummy Loads