Repository: flutter
Issue: WidgetTester.dragFrom touchSlop parameters seem to be broken
Labels: a: tests,framework,d: api docs,has reproducible steps,P2,found in release: 2.5,found in release: 2.6,team-framework,triaged-framework

## Steps to Reproduce

1. Have a few gestures participating in the arena
2. Set the the `touchSlopY` to `<=18.0`

**Expected results:** touch slop to be successfully configured, and test passing

**Actual results:** no matter how big the drag offset actually is - it can't drag and the test fails. The test passes for values of slop `>=19.0`

<details>
  <summary>Code sample</summary>

```dart
import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('Drag test', (WidgetTester tester) async {
    final ScrollController controller = ScrollController();
    final List<int> list = List<int>.generate(40, (int index) => index);
    await tester.pumpWidget(
      MaterialApp(
        home: Material(
          color: Colors.transparent,
          child: ListView.builder(
            controller: controller,
            itemExtent: 100.0,
            itemCount: list.length,
            itemBuilder: (BuildContext context, int index) => ListTile(
              title: Text(list[index].toString()),
              onTap: () {},
            ),
          ),
        ),
      ),
    );
    const double slop = 18;
    await tester.dragFrom(
      const Offset(100.0, 100.0),
      const Offset(0.0, -100.0),
      touchSlopY: slop,
    );
    expect(controller.offset, 100.0 - slop);
  });
}
```

</details>

<details>
  <summary>Logs</summary>

```
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following TestFailure object was thrown running a test:
  Expected: <82.0>
  Actual: <0.0>

When the exception was thrown, this was the stack:
#4      main.<anonymous closure> (file:///C:/dev/projects/issues/test/widget_test.dart:30:5)
<asynchronous suspension>
<asynchronous suspension>
(elided one frame from package:stack_trace)

This was caught by the test expectation on the following line:
  file:///C:/dev/projects/issues/test/widget_test.dart line 30
The test description was:
  Drag test
════════════════════════════════════════════════════════════════════════════════════════════════════
Test failed. See exception logs above.
The test description was: Drag test

✖ Drag test
```

```
[√] Flutter (Channel master, 2.6.0-12.0.pre.273, on Microsoft Windows [Version
    10.0.19041.1237], locale ru-RU)
    • Flutter version 2.6.0-12.0.pre.273 at C:\dev\src\flutter
    • Upstream repository git@github.com:nt4f04und/flutter.git
    • FLUTTER_GIT_URL = git@github.com:nt4f04und/flutter.git
    • Framework revision 1d102be762 (8 hours ago), 2021-10-08 23:23:04 +0530  
    • Engine revision a2773d5ec3
    • Dart version 2.15.0 (build 2.15.0-178.0.dev)

[!] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at C:\Users\danya\AppData\Local\Android\sdk
    X cmdline-tools component is missing
      Run `path/to/sdkmanager --install "cmdline-tools;latest"`
      See https://developer.android.com/studio/command-line for more details.   
    X Android license status unknown.
      Run `flutter doctor --android-licenses` to accept the SDK licenses.       
      See https://flutter.dev/docs/get-started/install/windows#android-setup for
      more details.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[√] Visual Studio - develop for Windows (Visual Studio Community 2019 16.7.7)
    • Visual Studio at C:\Program Files (x86)\Microsoft Visual
      Studio\2019\Community
    • Visual Studio Community 2019 version 16.7.30621.155
    • Windows 10 SDK version 10.0.19041.0

[√] Android Studio (version 4.1)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)

[√] IntelliJ IDEA Community Edition (version 2020.3)
    • IntelliJ at C:\Program Files\JetBrains\IntelliJ IDEA Community Edition
      2020.3.3
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart

[√] VS Code (version 1.61.0)
    • VS Code at C:\Users\danya\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.27.0

[√] Connected device (4 available)
    • sdk gphone x86 (mobile) • emulator-5554 • android-x86    • Android 11 (API
      30) (emulator)
    • Windows (desktop)       • windows       • windows-x64    • Microsoft Windows      [Version 10.0.19041.1237]
    • Chrome (web)            • chrome        • web-javascript • Google Chrome
      94.0.4606.71
    • Edge (web)              • edge          • web-javascript • Microsoft Edge
      94.0.992.38

! Doctor found issues in 1 category.
```

</details>