How to setup calling a function on a mock with a mock as parameter (with NNBD)?

[denniskaselow]

Using 5.0.0-nullsafety.0.

I have a class Foo and a class Bar which I want to mock for use in the class I want to test. Both classes interact with each other. Before nullsafety I could simply set this up, but I'm not sure how I am supposed to do that post-NNBD because mockito itself uses methods on the mocks that aren't mocked and I don't think I should mock stuff so mockito works.

Example:

// foobar.dart
class Foo {
  String process(Bar bar) => 'result';
}

class Bar {}

// foobar_test.dart
import 'package:mockito/annotations.dart';
import 'package:mockito/mockito.dart';
import 'package:test/test.dart';

import 'package:foobar/foobar.dart';
import 'world_test.mocks.dart';

@GenerateMocks([
  Foo,
  Bar
], customMocks: [
  MockSpec<Foo>(as: #MockFoo2, returnNullOnMissingStub: true),
  MockSpec<Bar>(as: #MockBar2, returnNullOnMissingStub: true),
])
void main() {
  test('default mock', () {
    final foo = MockFoo();
    final bar = MockBar();
    when(foo.process(bar)).thenReturn('mockedResult');

    foo.process(bar);
  });
  test('null mock', () {
    final foo = MockFoo2();
    final bar = MockBar2();
    when(foo.process(bar)).thenReturn('mockedResult');

    foo.process(bar);
  });
}

The code fails in the foo.process(bar); line.

The resulting error of the default mock test is: NoSuchMethodError: Object has no == method accepting arguments (_)

The resulting error of the null mock test is: type 'Null' is not a subtype of type 'bool'

The important part of the stacktrace is this:

test\foobar_test.mocks.dart 62:13      MockBar2.==
package:collection/src/equality.dart 87:45          DefaultEquality.equals
package:collection/src/equality.dart 458:18         DeepCollectionEquality.equals
package:mockito/src/invocation_matcher.dart 184:18  _MatcherEquality.equals
package:collection/src/equality.dart 177:29         ListEquality.equals
package:mockito/src/invocation_matcher.dart 158:12  _InvocationMatcher.matches
package:mockito/src/mock.dart 141:27                Mock.noSuchMethod.<fn>

If I do something stupid like when(bar == bar).thenReturn(true); I'll just get a stackoverflow.

[srawlins]

Great catch. This is related to #305, in which it is requested that Object.== be auto-stubbed instead of throwing.

The resulting error of the default mock test is: NoSuchMethodError: Object has no == method accepting arguments (_)

Right, so without the returnNullOnMissingStub feature, mockito has called MockBar.==, which used to return null (unless you called throwOnMissingStub) and now throws, unless you'd stubbed ==. We might be able to tiptoe around == with an is check or an identical call or something... Hopefully we can make a solution that doesn't involve new code for you to write, like a stub.

The resulting error of the null mock test is: type 'Null' is not a subtype of type 'bool'

This test uses the old behavior (returnNullOnMissingStub), in which null is returned for MockBar.==. Fixing the above case might fix this, but generally speaking, this is why the default behavior is changed; null is no longer the safe return value it once was.

[denniskaselow]

I wouldn't call returnNullOnMissingStub the old behavior because those tests work with stable mockito. Things like ==, runtimeType and toString() never returned null. They just used the real implementation of the Mock or Object class and couldn't even be stubbed.

[denniskaselow]

Those functions (hashcode, toString()) and operators (==) still exist on the Mock class (https://github.com/dart-lang/mockito/blob/master/lib/src/mock.dart#L155) and are maybe overridden by mistake because of #297? (and I'd not override runtimeType either) And I'd very much prefer it if that old behavior would be kept. If possible.

[srawlins]

@denniskaselow You're completely right. The solution is to stop overriding any methods defined by Mock or inherited by Mock, (get hashCode, operator ==, toString(), get runtimeType).

[srawlins]

This is fixed in 5.0.0-nullsafety.1.

[radvansky-tomas]

I have still this issue in 5.0.0
'Object.==' ('bool Function(Object)') isn't a valid concrete implementation of 'CollectionReference.==' ('bool Function(dynamic)').

[srawlins]

@radvansky-tomas I don't think your error is related to this issue.

[MilanObrenovic]

I still have this issue in mockito ^5.0.14

Add a stub for this method using Mockito's 'when' API, or generate the mock for MockIDatasource with 'returnNullOnMissingStub: true'.

[srawlins]

@MilanObrenovic I don't see any reason why your issue is related to this one. Feel free to open a new bug with a minimal reproduction case.