Flutter: Test that a specific exception is thrown

Question

in short, throwsA(anything) does not suffice for me while unit testing in dart. How to I test for a specific error message or type?

Here is the error I would like to catch:

class MyCustErr implements Exception {
  String term;

  String errMsg() => 'You have already added a container with the id 
  $term. Duplicates are not allowed';

  MyCustErr({this.term});
}

here is the current assertion that passes, but would like to check for the error type above:

expect(() => operations.lookupOrderDetails(), throwsA(anything));

This is what I want to do:

expect(() => operations.lookupOrderDetails(), throwsA(MyCustErr));

Answer 1

In case anyone wants to test with an async function like I had to do all you need to do is add async keyword in the expect, bearing in mind that the lookupOrderDetails is an async function:

expect(() **async** => **await** operations.lookupOrderDetails(), throwsA(const TypeMatcher<MyCustErr>()));

expect(() **async** => **await** operations.lookupOrderDetails(), isInstanceOf<MyCustErr>()));

It still uses Gunter's answer which is very good!

Answer 2

This should do what you want:

expect(() => operations.lookupOrderDetails(), throwsA(const TypeMatcher<MyCustErr>()));

expect(() => operations.lookupOrderDetails(), isInstanceOf<MyCustErr>());

if you just want to check for exception check this answer:

Answer 3

After `TypeMatcher<>' has been deprecated in Flutter 1.12.1 I found this to work:

expect(() => operations.lookupOrderDetails(), throwsA(isInstanceOf<MyCustErr>()));

Answer 4

First import correct package 'package:matcher/matcher.dart';

expect(() => yourOperation.yourMethod(),
      throwsA(const TypeMatcher<YourException>()));