Get a set of visually-similar fuses that claim to be the same rating. (Visually because you need the shape to be the same). When testing a few to destruction, record the temperature of the fusing element and resistance and power over time. Also measure the temperature at operating current.

Now the fuse you want to have the utmost trust in, test it at at half the time it should fail for a given i^2t. The temperature, resistance, and power curve should match the ones you tested destructively. The temperature at operating current should also be similar. If so, you can expect it to fail the way your destructively-tested fuses did.

Now, if you trust the metal composition and fusing element shape, a simple resistance meter will tell you if two fuses will behave the same.

You can destructively test samples out of a box of them. But even then the proper current profile that a fuse is supposed to accept or block is far from obvious or intuitive. Reading the spec helps. And then you still have the problem of supplying an acceptable sequence to get a correct result as you desired.

Another option is to experimentally send through various current profiles so that you - more intuitively - get a better understanding of whether your thinking of what you want to protect from, might actually happen.

I would use a variable power supply, amp meter and some sacrificial fuses. Slowly turn up the voltage while watching amps on the circuit until it blows? Or simply apply the rated amps (with current controlled power supply) to verify if/when the fuse blows.

I have a multiple-fuse assortment kit that was a great (too good?) deal from AliExpress. Now I'm thinking I need to do some of those tests myself to verify their rating.

You could... whoah, wait a second... isn't this one of the few places where that interview question of "determine the durability of N objects by dropping them from different floors in a building in a minimum of attempts" may actually be relevant?

Terminally.

destructively