Function to determine if two numbers are nearly equal when rounded to n significant decimal digits

Question

I have been asked to test a library provided by a 3rd party. The library is known to be accurate to n significant figures. Any less-significant errors can safely be

Answer 1

Oren Shemesh got part of the problem with the problem as stated but there's more:

assert nearlyequal( 0.0, 1e-15, 5 )

also fails the second definition (and that's the definition I learned in school.)

No matter how many digits you are looking at, 0 will not equal a not-zero. This could prove to be a headache for such tests if you have a case whose correct answer is zero.