i met with a question like this:
A: stop eating the cake!
B: I ________________.
"was just tasting it" or " just tasted " which is better?
I don't agree with Sandhya that there's any such implication. "Was tasting" sounds right, I think because we use the progressive tense for an action that's in progress when something else happens. Here, the "something else" isn't stated, but is understood as A interrupting B eating.
If A had noticed some of the cake was missing but hadn't seen A eating it, so there was an interval between actions, the simple past tense, "tasted", would be correct.