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WidgetTest.pump(elapsedTime) doesn't advance time reliably #348
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Activity
It seemed like addling
tester.async.flushMicrotasks();calls after pump(), would run the completer that advanced the performance's timeline. That doesn't appear to be the case.Pump already calls flushMicrotasks. Maybe the issue is that flushMicrotasks doesn't fully drain the microtask queue? The docs say it should:
/// Runs all remaining microtasks, including those scheduled as a result of /// running them, until there are no more microtasks scheduled. /// /// Does not run timers.The reason is that performances don't actually start when you call forward() or reverse(), they start at the next frame (the next call to pump(), in tests). This is good, it means all the animations will have consistent frame-aligned timings. If we didn't do this, then five animations started in the same 16ms interval might all have different start times.
Thus, just adding the two lines marked
<----below solves the problem: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(); tester.pump(); // <---- 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=${performance.progress} is actually 1.0"); performance.reverse(); tester.pump(); // <---- tester.pump(new Duration(seconds: 1)); print("performance.progress=${performance.progress} expect 0.0"); tester.pump(new Duration(seconds: 1)); print("performance.progress=${performance.progress} is actually 0.0"); }); }); }
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on Sep 7, 2021
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.