the new _IconButtonM3 is reusing the parent widget key. (line 500 of icon_button.dart)

      return _IconButtonM3(
        key: key,
        // ...
      );

which can make some tests fail, "expected 1 widget with key x but found 2" .

As explained in a similar issue where flutter duplicates keys, here: #103266 , I'm under the impression that flutter should not reuse keys. I could be wrong though as this seems to be something recurring. It's definitely unexpected though.

This was caught by our test suite updating to latest master.