Obsolete ELCBs that sensed the current in the protective Earth conductor may have used a test button load between Live and Earth, but the test button on a RCD does *NOT* apply a load between Live and Earth. Many RCDs don't even have an earth connection, and for those that do, it would be hazardous to have a test button that would make the protective Earth live if it had an O/C fault in the feed to the RCD. Instead, it applies a load from Live on the downstream side to Neutral on the feed, which results in a current imbalance between Live and Neutral through the device, simulating the same fault current to ground.
There's also the issue of repeated tripping. If the RCD is carrying close to its rated current, it may well be degraded by tripping it and failure within as little as 50 trip events is entirely possible. Any RCD that meets the standards required in developed countries should be designed to fail safe, so the usual consequence is it fails open. A thermal RCBO that is repeatedly tripped is likely to become more sensitive to current due to contact damage increasing its self-heating.
As 100mA RCDs are usually used as the main supply disconnect, replacing them is a total PITA, as you will have to break the tamperproof seal on the electricity company's fuse to isolate the supply, and will need to get the seal replaced before the meter reader sees its missing. Therefore tripping them deliberately more frequently than for an annual test is a really bad idea.