Xunit: Exception if fixtures have more than one constructor with arguments

[joaomsa]

For some tests I want to share a fixture directly, other times I want to use it to build up a more complex fixture and pass in some parameters.

Ideally for me xUnit should use the default parameterless constructor if it's available instead of throwing an exception

```c#
public class ConfigurationFixture
{
public string ConnectionString { get; }

    public ConfigurationFixture()
    {
        var timestamp = DateTimeOffset.Now.ToUnixTimeSeconds();
        ConnectionString = $"Server=(localdb)\\mssqllocaldb;Database=Test_{timestamp};Trusted_Connection=True;MultipleActiveResultSets=true";       
    }
}

public class DatabaseFixture
{
    public DatabaseFixture()
        : this(new ConfigurationFixture())
    {
    }

    public DatabaseFixture(ConfigurationFixture configFixture)
    {
        // Setup db with connection string
    }
}

public class WebserverFixture
{
    public WebserverFixture()
    {
        var configFixture = new ConfigurationFixture();
        var dbFixture = new DatabaseFixture(configFixture);

        // Setup webserver and database with same connection string well
    }
}

public class UnitTests : IClassFixture<DatabaseFixture>
{
    public UnitTests(DatabaseFixture dbFixture)
    {
    }

    [Fact]
    public void Run()
    {
        Assert.True(true);
    }
}

public class IntegrationTests : IClassFixture<WebserverFixture>
{
    public IntegrationTests(WebserverFixture serverFixture)
    {
    }

    [Fact]
    public void Run()
    {
        Assert.True(true);
    }
}

throws an exception:

Test Name: Tests.UnitTests.Run
Test FullName: Tests.UnitTests.Run
Test Source: C:Users\Joao Sa\Source\Repos\TestsClass1.cs : line 51
Test Outcome: Failed
Test Duration: 0:00:00.001

Result StackTrace:
----- Inner Stack Trace #1 (Xunit.Sdk.TestClassException) -----

----- Inner Stack Trace #2 (Xunit.Sdk.TestClassException) -----
Result Message:
System.AggregateException : One or more errors occurred. (Class fixture type Tests.DatabaseFixture' may only define a single public constructor.) (The following constructor parameters did not have matching fixture data: DatabaseFixture dbFixture)
---- Class fixture type 'Tests.DatabaseFixture' may only define a single public constructor.
---- The following constructor parameters did not have matching fixture data: DatabaseFixture dbFixture

```

[bradwilson]

xUnit.net does not necessarily prefer the parameterless constructor, since there are ways to provide constructor arguments to fixtures (for example, for other fixtures).

[uberintj]

@bradwilson: not related to this issue, but related to your comment, where can I find information on 'ways to provide constructor arguments to fixtures'?

[bradwilson]

@uberintj You can pass collection fixtures into the constructor of a class fixture. The code which does the mapping is here:

https://github.com/xunit/xunit/blob/bccfcccf26b2c63c90573fe1a17e6572882ef39c/src/xunit.execution/Sdk/Frameworks/Runners/XunitTestClassRunner.cs#L60-L91

[angshuman]

If I am using a class fixture like below, how to I pass this ClassFixtureMappings parameter? I am guessing override of some sort. An example would really help.

public sealed class MyTests: IClassFixture<TestFixture>, IDisposable