testTextInput property Null safety
Returns the TestTextInput singleton.
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;