where I can find a FREE tool that I may use to test my circuits

where can I get a free Cadillac? is an equally valid question.

"test my circuits" (note that I have emphasized the pluaral) relates to equipment costing (for useable solutions) hundereds of thousands of dollars. The classic example is the "bed of nails" which is not even close to being optimal. If somebody were to give away for free what he could sell for hundereds of thousands of dollars per pop, I would suggest he moved to the insane asylum voluntarily before being committed.

Were you to do something to test a specific circuit, then solutions could, maybe, be found. It is, for instance, possible to add circuitry to make testing possible.

Wikipedia says such stuff falls under EDA (Electronic Design Automation)
and - as usual - Wikipedia is wrong. Testing and design have NOTHING to do with each other except the issue of "designing for test". As an example of "designing for test", I have, in come crirical positions a very low ohmic resistor instead of just a PCB trace to allow the testing device to 'see' an actual point.

Erik