Returns the TestTextInput singleton.
Typical app tests will not need to use this value. To add text to widgets like TextField or TextFormField, call enterText.
Some of the properties and methods on this value are only valid if the binding's TestWidgetsFlutterBinding.registerTestTextInput flag is set to true as a test is starting (meaning that the keyboard is to be simulated by the test framework). If those members are accessed when using a binding that sets this flag to false, they will throw.
TestTextInput get testTextInput => binding.testTextInput;