To expand upon @jdthood's answer...

If the interface is already up, you can still use this method to validate the /etc/network/interfaces file. For example, assuming you have an error, you may see something like this:

$ sudo ifup --no-act eth0
/etc/network/interfaces:11: unknown method
ifup: couldn't read interfaces file "/etc/network/interfaces"
Apparently there's an error on line 11. Great. Thank heavens I didn't bounce the networking only to lose SSH access!

If all is fine, you will see:

$ sudo ifup --no-act eth0
ifup: interface eth0 already configured