Javadoc
Checks whether the estimator can handle instance weights. This test
compares the estimator performance on two datasets that are identical
except for the training weights. If the results change, then the estimator
must be using the weights. It may be possible to get a false positive from
this test if the weight changes aren't significant enough to induce a
change in estimator performance (but the weights are chosen to minimize the
likelihood of this).