TestTextInput state reset

The state of a TestTextInput instance, a stub for the system's onscreen keyboard, is now reset between tests.

The Flutter test framework uses a class called TestTextInput to track and manipulate editing state in a widgets test. Individual tests can make calls that modify the internal state of this object, sometimes indirectly (such as by setting their own handlers on SystemChannels.textInput). Subsequent tests might then check the state of WidgetTester.testTextInput and get unexpected values.

The state of WidgetTester.testTextInput is now reset before running a testWidgets test.

Tests that relied on dirty state from a previously run test must be updated. For example, the following test, from packages/flutter/test/material/text_field_test.dart in the 'Controller can update server' test, previously passed because of a combination of dirty state from previous tests and a failure to actually set state in cases where it should have been set.

Code before migration:

In a widgetsTest, before actually changing text on a text editing widget, this call might have succeeded:

    expect(tester.testTextInput.editingState['text'], isEmpty);

Code after migration:

Either remove the call entirely, or consider using the following to assert that the state hasn't been modified yet:

    expect(tester.testTextInput.editingState, isNull);

Landed in version: 1.16.3
In stable release: 1.17

API documentation:

• TestTextInput
• WidgetTester

Relevant issue:

• Randomize test order to avoid global state

Relevant PR:

• Reset state between tests

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