Which statement is NOT true about black box testing?

Group of answer choices

We can strengthen input partition testing by applying the shotgun method; this provides additional confidence that there are more inputs that work on the program under test.

Black box testing can be done through coverage tests on the input, output, and functionality.

Exhaustive, input partitioning, and shotgun are all systematic black box testing methods.

Usually, when choosing test inputs, we wish to only vary one variable $($possible cause$)$ at a time, keeping everything else unchanged to ensure the isolation of variables.