I’m using xUnit, SubSpec and FakeItEasy for my unit tests. I’ve so far created some positive unit tests like the following:
"Given a Options presenter"
.Context(() =>
presenter = new OptionsPresenter(view,
A<IOptionsModel>.Ignored,
service));
"with the Initialize method called to retrieve the option values"
.Do(() =>
presenter.Initialize());
"expect the view not to be null"
.Observation(() =>
Assert.NotNull(view));
"expect the view AutoSave property to be true"
.Observation(() => Assert.True(view.AutoSave));
But now I want to write some negative unit tests and check that certain methods don't get called, and an exception is thrown
e.g.
"Given a Options presenter"
.Context(() =>
presenter = new OptionsPresenter(view,
A<IOptionsModel>.Ignored,
service));
"with the Save method called to save the option values"
.Do(() =>
presenter.Save());
"expect an ValidationException to be thrown"
.Observation(() =>
// TODO
);
"expect an service.SaveOptions method not to be called"
.Observation(() =>
// TODO
);
I can see FakeItEasy has a MustNotHaveHappened extension method, and xUnit has an Assert.Throws method.
But how do I put it all together?
The exception I want to test for should occur when the Save method is called. So I’m guessing I should wrap an Assert.Throws method around the presenter.Save() method call, but I thought the presenter.Save method should be called in the .Do(() => ...
Can you please advise if my unit test should look like below or something else?
"Given a Options presenter"
.Context(() =>
presenter = new OptionsPresenter(view,
model,
service));
"expect the Presenter.Save call to throw an Exception"
.Observation(() =>
Assert.Throws<FluentValidation.ValidationException>(() => presenter.Save()));
"expect the Service.SaveOptions method not to be called"
.Observation(() =>
A.CallTo(() => service.SaveOptions(A<IOptionsModel>.Ignored)).MustNotHaveHappened());
Many thanks
I've not heard of fakeItEasy or subSpec (You're tests look pretty funky, so I might check these out :)). However, I do use xUnit so this may be helpful:
I use Record.Exception with Assert.ThrowsDelegate
So something like:
[Fact]
public void Test()
{
// Arange
// Act
Exception ex = Record.Exception(new Assert.ThrowsDelegate(() => { service.DoStuff(); }));
// Assert
Assert.IsType(typeof(<whatever exception type you are looking for>), ex);
Assert.Equal("<whatever message text you are looking for>", ex.Message);
}
Hope that helps.