Hi Can anyone tell me how or what equipment is needed to test a capacitor
A capacitor meter would be suitable. Some multimeters have a built-in capacitor tester.
For electrolytic capacitors an ESR tester is useful.
is there a visible sign that a capacitor is faulty,
Yes, if it is mechanically defect, e.g. broken or in the case of electrolytic capacitors if the endcap has bulged or, worse, broken and has leaked electrolytic fluid.
It is
kind of a standard procedure to replace electrolytic capacitors in older electronic devices if they operate erratically or not at all.
Ceramic capacitors usually fail only if they are mechanically damaged, although there is always the possibility of an invisible internal short or open circuit.
Foil capacitors are rather robust, but mechanical damage also happens to them.
We may be able to help you in more detail if you provide more information on the type of device and defect you are working on.