Autofixture generates a custom list

Question

Here is my goal:

public class Symbol { private readonly string _identifier; private readonly IList<Quote> _historicalQuotes; public Symbol(string identifier, IEnumerable<Quote> historicalQuotes = null) { _identifier = identifier; _historicalQuotes = historicalQuotes; } } public class Quote { private readonly DateTime _tradingDate; private readonly decimal _open; private readonly decimal _high; private readonly decimal _low; private readonly decimal _close; private readonly decimal _closeAdjusted; private readonly long _volume; public Quote( DateTime tradingDate, decimal open, decimal high, decimal low, decimal close, decimal closeAdjusted, long volume) { _tradingDate = tradingDate; _open = open; _high = high; _low = low; _close = close; _closeAdjusted = closeAdjusted; _volume = volume; } } 

I need a Symbol instance populated with a Quote list.

In my test, I want to check that I can return all quotes whose closing price is above a certain value or higher. Here is my test:

 [Fact] public void PriceUnder50() { var msftIdentifier = "MSFT"; var quotes = new List<Quote> { new Quote(DateTime.Parse("01-01-2009"), 0, 0, 0, 49, 0, 0), new Quote(DateTime.Parse("01-02-2009"), 0, 0, 0, 51, 0, 0), new Quote(DateTime.Parse("01-03-2009"), 0, 0, 0, 50, 0, 0), new Quote(DateTime.Parse("01-04-2009"), 0, 0, 0, 10, 0, 0) }; _symbol = new Symbol(msftIdentifier, quotes); var indicator = new UnderPriceIndicator(50); var actual = indicator.Apply(_symbol); Assert.Equal(2, actual.Count); Assert.True(actual.Any(a => a.Date == DateTime.Parse("01-01-2009"))); Assert.True(actual.Any(a => a.Date == DateTime.Parse("01-04-2009"))); Assert.True(actual.Any(a => a.Price == 49)); Assert.True(actual.Any(a => a.Price == 10)); } 

OK

Now I want to do this using Autofixture, im a real beginner. I read almost everything I could on the Internet about this tool (author’s blog, frequently asked questions about codeple, github source code). I understand the main features of car chemistry, but now I want to use autofixture in my real project. Here is what I have tried so far.

 var msftIdentifier = "MSFT"; var quotes = new List<Quote>(); var random = new Random(); fixture.AddManyTo( quotes, () => fixture.Build<Quote>().With(a => a.Close, random.Next(1,49)).Create()); quotes.Add(fixture.Build<Quote>().With(a => a.Close, 49).Create()); _symbol = new Symbol(msftIdentifier, quotes); // I would just assert than 49 is in the list Assert.True(_symbol.HistoricalQuotes.Contains(new Quote... blabla 49)); 

Ideally, I would prefer to directly create a Symbol binding, but I do not know how to set up my list of quotes. And I'm not sure that my test is general, because in another test I will need to check that the specific value is higher and not lower, so I'm going to duplicate the “device code” and manually add the quote = 51.

So my questions are:

1 - How can I use the car receiver?

2 - Is it possible to improve the way I use auto-set-top boxes in my example?

Answer 1

AutoFixture was originally created as a test development tool (TDD), and TDD is feedback . In the spirit of GOOS, you should listen to your tests . If tests are hard to write, you should consider your API design. AutoFixture tends to reinforce that kind of feedback , and that's what it tells me.

Make comparison easier

Firstly, not related to AutoFixture, the Quote class simply accesses the correct value object , so I override Equals to make it easier to compare expected and actual instances:

 public override bool Equals(object obj) { var other = obj as Quote; if (other == null) return base.Equals(obj); return _tradingDate == other._tradingDate && _open == other._open && _high == other._high && _low == other._low && _close == other._close && _closeAdjusted == other._closeAdjusted && _volume == other._volume; } 

(Remember to also override GetHashCode .)

Copy and update

The above test attempt seems to imply that we lack the ability to change one field while maintaining a constant constant . Taking a cue from functional languages, we can introduce a way to do this in the Quote class itself:

 public Quote WithClose(decimal newClose) { return new Quote( _tradingDate, _open, _high, _low, newClose, _closeAdjusted, _volume); } 

This type of API is generally very useful for Value objects, to the extent that I always add such methods to my Value objects.

Do the same with Symbol :

 public Symbol WithHistoricalQuotes(IEnumerable<Quote> newHistoricalQuotes) { return new Symbol(_identifier, newHistoricalQuotes); } 

This makes it easy to ask AutoFixture anything you don’t like, while at the same time explicitly specifying only what you need.

Testing with AutoFixture

The original test can now be rewritten as:

 [Fact] public void PriceUnder50() { var fixture = new Fixture(); var quotes = new[] { fixture.Create<Quote>().WithClose(49), fixture.Create<Quote>().WithClose(51), fixture.Create<Quote>().WithClose(50), fixture.Create<Quote>().WithClose(10), }; var symbol = fixture.Create<Symbol>().WithHistoricalQuotes(quotes); var indicator = fixture.Create<UnderPriceIndicator>().WithLimit(50); var actual = indicator.Apply(symbol); var expected = new[] { quotes[0], quotes[3] }; Assert.Equal(expected, actual); } 

Only parts of the test case that you care about are indicated in this test, while AutoFixture takes care of all other values ​​that do not affect the test case. This makes the test more reliable as well as more readable.