Is having an EEG enuf to test for epilepsy?

See below. Sometimes. An eeg is not always abnormal in patients with seizures. Sometimes, a prolonged eeg with video monitoring is needed.
If during a spell. If the eeg was running during a spell, that can be sufficient to characterize the spell as epileptic or non-epileptic. That being said, eegs done between spells are often normal, even in people known to have epilepsy. Additionally, if epilepsy is confirmed, often an MRI is done to rule out the possibility of a mass lesion acting as a source.