Unit testing in Flutter passing BuildContext

Question

I have a method in a Dart class, which accepts BuildContext parameter, as follows:

class MyClass {

  <return_type> myMethodName(BuildContext context, ...) {
        ...
        doSomething
        return something;
    }
}

I want to test that the method works as expected:

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:mockito/mockito.dart';
...

void main() {
  MyClass sut;

  setUp(() {
    sut = MyClass();
  });

  test('me testing', () {

    var actual = sut.myMethodName(...);        

    expect(actual, something);
  });
}

Of course, it won't work, because the method myMethodName needs a parameter BuildContext type. This value is available throughout the application itself, but not sure where to get that from in my unit tests.

Answer 1

You can actually mock the BuildContext so the test will run headless. I think it's better but might be not a solution that you are looking for.

BuildContext is an abstract class therefore it cannot be instantiated. Any abstract class can be mocked by creating implementations of that class. If I take your example then the code will look like this:

class MockBuildContext extends Mock implements BuildContext {}

void main() {
   MyClass sut;
   MockBuildContext _mockContext;

   setUp(() {
     sut = MyClass();
     _mockContext = MockBuildContext();
   });

   test('me testing', () {

   var actual = sut.myMethodName(_mockContext, ...);        

   expect(actual, something);
  });
}

(Note that this requires the Mockito package: https://pub.dev/packages/mockito).