WidgetTest.pump(elapsedTime) doesn't advance time reliably #348
Description
Using WidgetTest.pump(elapsedTime) to advance animations and completions in a test can be difficult because just calling the function once doesn't necessarily roll all of the test's state forward by the specified time. The unit test below illustrates a simple version of the problem: it's necessary to call pump(1 second) twice to get the 200ms performance from one end to the other. More complex widgets, see for example snack_bar_test.dart, require more blind test pumping.
import 'package:flutter/animation.dart';
import 'package:flutter/widgets.dart';
import 'package:test/test.dart';
import 'widget_tester.dart';
void main() {
test('Time does not move', () {
testWidgets((WidgetTester tester) {
tester.pumpWidget(new Container());
Performance performance = new Performance(duration: const Duration(milliseconds: 200))
..forward();
print("performance.progress=${performance.progress} expect 0.0");
tester.pump(new Duration(seconds: 1));
print("performance.progress=${performance.progress} expect 1.0");
tester.pump(new Duration(seconds: 1));
print("performance.progress=${performance.progress} is actually 1.0");
performance.reverse();
tester.pump(new Duration(seconds: 1));
print("performance.progress=${performance.progress} expect 0.0");
tester.pump(new Duration(seconds: 1));
print("performance.progress=${performance.progress} is actualy 0.0");
});
});
}