Ten people taste wine A and wine B. Let $X$ denote the number
who prefer A. Assume that all the others indicate a preference
for B. The people are a random sample. If $X=10$, and we test
the null hypothesis of no difference in preference between the
wines (vs. two-sided alternative), the $p$-value is equal to
0.0020. I don't get how one comes to the conclusion that the
p-value is 0.0020. Are you supposed to use the one sample test
for proportion?