TLDR;
Go to the code example: code.
This is a feature in Xunit that I think people arent using enough. There are many times that you can get away with having a few parameters into a test with the attribute InlineData, and it will look something like this:
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[Theory]
[InlineData("")]
[InlineData(" ")]
[InlineData(null)]
public void Given_Something_Should_Throw_Exception(string name)
{
var act = () =>
{
//Do seomthing with name
};
act.Should().Throw<ArgumentException>("*name*");
}
A parameterized test is common as above, but when it comes to the fact that you would like to have a collection of some sort as a parameter, I dont see people use MemberData attribute together with TheoryData.
How it works is quite simple; foreach item in your TheoryData is one test case. For example, let’s say you want to test a method that takes in a string as a parameter to not be null, empty or only spaces. You could create a source of data with 3 items, and reference that as your MemberData for your Theory like below:
Example code
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public class TestData
{
public static TheoryData<string> StringNullEmptyAndWhiteSpace =>
new TheoryData<string>()
{
{ "" },
{ null },
{ " " },
};
}
public class FubarTests
{
[Theory]
[MemberData(nameof(TestData.StringNullEmptyAndWhiteSpace), MemberType = typeof(TestData))]
public void Given_Something_Should_Throw_Exception(string name)
{
var act = () =>
{
//Do seomthing with name
};
act.Should().Throw<ArgumentException>("*name*");
}
}
The assertion above is written with FluentAssertions, one of my favourite libraries for assertions!
Small note here for the attribute, the propert MemberType is only required if you have “TestData” outside the class you want to use it in. If you would create a property in the same class as your test, you dont need to set this property.
More Complex parameters?
As TheoryData is generic you can basically add whatever model you want to have, so you could also have a parameter that is a list, for ex:
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public static TheoryData<IEnumerable<string>> ListAsParameter =>
new TheoryData<IEnumerable<string>>()
{
new [] { "" , null, " " ,}
};
This way you can with ease have more complex parameters to your Theory lists for example, that InlineData dosent support!
Frankly I dont know, why I dont see this small feature used more often, also, I see people use this with objects instead of actually classes.