"callback" is redundant – it's a TestCallback object and
it takes a type of callback anyway.
"assertNextIs" is shorter than expectCallback, and more
directly explicit than "expect", but it's also 3 words
and very different from previous usage.
Using expect() is a little bit less in-your-face obvious,
but it's simple, familiar, and short.
Test: CtsNetTestCases
FrameworksNetIntegrationTests
FrameworksNetTests
NetworkStackTests
Bug: 157405399
Change-Id: I6c8c85a8be3895dd8f0ef681faa4a8b2b4f2f493
b7e2284acf