Flutter: Test that a specific exception is thrown
As of April 2021 this is the correct method.
CORRECT METHOD
import 'package:dcli/dcli.dart';
import 'package:test/test.dart';
/// GOOD: works in all circumstances.
expect(() => restoreFile(file), throwsA(isA<RestoreFileException>()));
Some examples show :
INCORRECT METHOD
import 'package:dcli/dcli.dart';
import 'package:test/test.dart';
/// BAD: works but not in all circumstances
expect(restoreFile(file), throwsA(isA<RestoreFileException>()));
Note the missing '() => ' after the expect.
The difference is that the first method will work for functions that return void whilst the second method won't.
So the first method should be the prefered technique.
To test for a specific error message:
CHECK CONTENTS OF EXCEPTION AS WELL
import 'package:dcli/dcli.dart';
import 'package:test/test.dart';
expect(
() => copy(from, to),
throwsA(predicate((e) =>
e is CopyException &&
e.message == 'The from file ${truepath(from)} does not exists.')));
After `TypeMatcher<>' has been deprecated in Flutter 1.12.1 I found this to work:
expect(() => operations.lookupOrderDetails(), throwsA(isInstanceOf<MyCustErr>()));
This should do what you want:
expect(() => operations.lookupOrderDetails(), throwsA(isA<MyCustErr>()));
if you just want to check for exception check this answer: