You adjust voltage in the bios.
Some memory needs extra voltage.
You can use cpu-z(or the memory makers specs from the website) to see how much is needed for most sticks. Memory is getting better so more and more just requires 1.5 volts(this is the default for DDR3)
Memtest+ to put it simple just places a data set into memory then reads it back if it does not match, the memory has failed. It will keep going and just keep adding errors as it finds them.
If you fail bad, you will know