Assert problem on widget_test.dart

[cristianopcortez]

I'm getting an assert test failure on run widget_test.dart:

The following TestFailure object was thrown running a test:
Expected: exactly one matching node in the widget tree
Actual: _TextFinder:<zero widgets with text "0" (ignoring offstage widgets)>
Which: means none were found but one was expected

The same question was made on stackoverflow too:

https://stackoverflow.com/questions/59450096/testing-dart-code-in-android-studio-no-widgets-involved-only-data-structures-a