Unit tests to catch exception in controller method

Question

I'm trying to learn unit testing in xUnit for ASP.NET Core projects. In order to achieve it, I have created simple ASP.NET Core project to perform tests on it. However I cannot get 100% cover of tests due to wrong testing an exception that's being caught inside controller method.

Here is my controller method I'm testing:

        [HttpGet]
        public async Task<IEnumerable<User>> GetUsers()
        {
            try
            {
                var users = await _repository.User.GetAllUsersAsync();
                return users;
            }
            catch (Exception e)
            {
                _logger.LogError($"Error in GetUsers: {e}");
                return null;
            }
        }

And here is my unit test method in xUnit:

        [Fact]
        public async Task GetUsers_WhenCalled_ReturnsCorrectAmountOfUsers()
        {
            //Arrange
            var mockRepo = new Mock<IRepositoryWrapper>();
            mockRepo.Setup(repo => repo.User.GetAllUsersAsync())
                .ReturnsAsync(GetTestUsers());
            var controller = new UsersController(mockRepo.Object, _logger, _service);

            //Act
            var result = await controller.GetUsers();

            //Assert
            var model = Assert.IsAssignableFrom<IEnumerable<User>>(result);
            model.Count().Should().Be(3);
            Assert.Throws<NullReferenceException>(() => 
            _controller.GetUsers().Exception);
        }

When I run tests, everything gets green status, however inside the controller class I cannot see a 'green tick' next to the lines with catch block scope. I'd really like to know how to write proper code for testing an exceptions inside catch blocks!

Nkosi · Accepted Answer · 2019-02-03 14:05:54Z

3

Another test is needed that will cause the exception to be thrown when being exercised.

For example

[Fact]
public async Task GetUsers_WhenCalled_HandlesException() {
    //Arrange
    var mockRepo = new Mock<IRepositoryWrapper>();
    mockRepo
        .Setup(repo => repo.User.GetAllUsersAsync())
        .ThrowsAsync(new InvalidOperationException());

    var controller = new UsersController(mockRepo.Object, _logger, _service);

    //Act
    var result = await controller.GetUsers();

    //Assert
    Assert.IsNull(result);
    //Can also assert what logger records
}

In the above example, when GetAllUsersAsync is invoked, it will throw an exception that will be caught in the try-catch and allow the code to flow as intended for the test.

edited Feb 3, 2019 at 14:05

answered Feb 3, 2019 at 13:59

Nkosi

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1 Comment

star213 Over a year ago

Thanks! That's actually works. All I had to do, was to add one more Mock for ILogger<UsersController> fake and pass it to UsersController initialization.

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