This is used to assess if 2 discrete (categorical) variables are independent for a population. This takes one population, one random sample, and two variables of interest.
The null hypothesis is that there is no association between smoking habit and hypertension status for the population of factory workers. That is, $$P(A \text{ and } B) \approx P(A)P(B)$$.
This is actually done the exact same way as the test of homogeneity test, just with different input data type.