How to deactivate or ignore layout overflow messages in Flutter widget tests?

Question

Tests run with the Ahem font, which is too big, and sometimes it overflows, breaking tests. Some tests don't care about overflow anyway, so there should be a way to deactivate them.

I have many tests which run OK in the simulator, but break in tests.

We are forced to prevent overflows for widgets which will never overflow in reality, or else provide fonts for the tests, instead of Ahem, just for the sake of not overflowing the tests. It makes no sense that overflow errors are tested, unless you are doing "overflow error tests".

How do I turn off these errors, or how do I make tests ignore them?

Answer 1

Based on @RémiRousselet answer, I developed a solution.

FlutterError.onError = _onError_ignoreOverflowErrors;

Function _onError_ignoreOverflowErrors = (
  FlutterErrorDetails details, {
  bool forceReport = false,
}) {
  assert(details != null);
  assert(details.exception != null);
  // ---

  bool ifIsOverflowError = false;

  // Detect overflow error.
  var exception = details.exception;
  if (exception is FlutterError)
    ifIsOverflowError = !exception.diagnostics
        .any((e) => e.value.toString().startsWith("A RenderFlex overflowed by"));

  // Ignore if is overflow error.
  if (ifIsOverflowError)
    print('Overflow error.');

  // Throw others errors.
  else
    FlutterError.dumpErrorToConsole(details, forceReport: forceReport);
};

This function ignores just overflow exceptions.

Answer 2

You cannot disable overflow specifically. But there are a few alternatives:

• Change the font to a "real" font. Your tests don't have to use Ahem font. The documentation is lacking, here's the issue that added this feature: https://github.com/flutter/flutter/issues/17700
• Change the virtual screen size. See How to test Flutter widgets on different screen sizes?
• set FlutterError.onError to null