Add a note about mockito to contribution guide (#1724)
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 749e48d..fa84388 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -96,6 +96,13 @@
cost constraints, pull requests from non-committers may not run all the tests
automatically.
+The plugins team prefers that unit tests are written using `setMockMethodCallHandler`
+rather than using mockito to mock out `MethodChannel`. For a list of the plugins that
+are still using the mockito testing style and need to be converted, see
+[issue 34284](https://github.com/flutter/flutter/issues/34284). If you are contributing
+tests to an existing plugin that uses mockito `MethodChannel`, consider converting
+them to use `setMockMethodCallHandler` instead.
+
Once you've gotten an LGTM from a project maintainer and once your PR has received
the green light from all our automated testing, wait for one the package maintainers
to merge the pull request and `pub submit` any affected packages.
