Sometimes it is necessary to optionally add a preparer. e.g. There are
many parameterized tests where one of the parameters is some additional
test setup but not every test provides it so it will default to the
"zero" value of whatever type is used for the test setup parameter
Migrating those tests to use test fixtures will typically require that
the test setup parameter be changed to a FixturePreparer, which by
default will be nil.
Attempting to use a nil FixturePreparer in the test fixtures will fail
so the OptionalFixturePreparer was added to wrap a possibly nil
FixturePreparer and thereby avoiding complicating each test with
similar logic.
Bug: 182885307
Test: m nothing
Change-Id: Ia12b2af2105fdc69af4e0b909a37a7b86f1af299
This change is in preparation for removing testing.T from TestResult.
Bug: 181070625
Test: m nothing
Change-Id: Ib51c7d4e5efdcbe0652df10b66140058a8bfa471
FixturePreparers is a bad name for a method that creates a collection
of FixturePreparers for a couple of reasons:
* Conventionally it would be used as the name for []FixturePreparer if
it is necessary to add behavior to that.
* There are many different types of collection, particularly when order
matters.
Bug: 181070625
Test: m nothing
Change-Id: I55394ff369375dcac2d7b72e4d803a4818762d36
Adds the test fixture support and converts a few tests to exercise the
code and show how it works.
Bug: 181070625
Test: m nothing
Change-Id: I0a2b40fff93b6041f9aa8c4ef0aba91da1bc8bf3
