Console Runner loads wrong .NET framework version when executing tests from multiple assemblies at once

When running tests from multiple assemblies with different target frameworks, the console runner seems to only load the highest framework version.

For example, I have two test projects: one with target framework version 3.5 and one with target framework version 4.0. The single test case in the 3.5 project looks like this:

using System;
using NUnit.Framework;

namespace Test35
{
    [TestFixture]
    public class TestFor35
    {
        [Test]
        public void Example()
        {
            Assert.AreEqual(new Version(2, 0, 0, 0), typeof(int).Assembly.GetName().Version);
        }
    }
}

The single test case in the 4.0 project looks like this:

using System;
using NUnit.Framework;

namespace Test40
{
    [TestFixture]
    public class TestFor40
    {
        [Test]
        public void Example()
        {
            Assert.AreEqual(new Version(4, 0, 0, 0), typeof(int).Assembly.GetName().Version);
        }
    }
}

Now, when I run the test assemblies individually, everything is fine:

D:\temp\Nunit.Test>nunit3-console.exe --noresult Test35\bin\Debug\Test35.dll
NUnit Console Runner 3.10.0 (.NET 2.0)
Copyright (c) 2019 Charlie Poole, Rob Prouse
Freitag, 9. August 2019 00:37:25

Runtime Environment
   OS Version: Microsoft Windows NT 10.0.18362.0
  CLR Version: 4.0.30319.42000

Test Files
    Test35\bin\Debug\Test35.dll


Run Settings
    DisposeRunners: True
    WorkDirectory: D:\temp\Nunit.Test
    ImageRuntimeVersion: 2.0.50727
    ImageRequiresX86: False
    ImageRequiresDefaultAppDomainAssemblyResolver: False
    NumberOfTestWorkers: 4

Test Run Summary
  Overall result: Passed
  Test Count: 1, Passed: 1, Failed: 0, Warnings: 0, Inconclusive: 0, Skipped: 0
  Start time: 2019-08-08 22:37:25Z
    End time: 2019-08-08 22:37:27Z
    Duration: 1.746 seconds

D:\temp\Nunit.Test>nunit3-console.exe --noresult Test40\bin\Debug\Test40.dll
NUnit Console Runner 3.10.0 (.NET 2.0)
Copyright (c) 2019 Charlie Poole, Rob Prouse
Freitag, 9. August 2019 00:37:41

Runtime Environment
   OS Version: Microsoft Windows NT 10.0.18362.0
  CLR Version: 4.0.30319.42000

Test Files
    Test40\bin\Debug\Test40.dll


Run Settings
    DisposeRunners: True
    WorkDirectory: D:\temp\Nunit.Test
    ImageRuntimeVersion: 4.0.30319
    ImageTargetFrameworkName: .NETFramework,Version=v4.0
    ImageRequiresX86: False
    ImageRequiresDefaultAppDomainAssemblyResolver: False
    NumberOfTestWorkers: 4

Test Run Summary
  Overall result: Passed
  Test Count: 1, Passed: 1, Failed: 0, Warnings: 0, Inconclusive: 0, Skipped: 0
  Start time: 2019-08-08 22:37:41Z
    End time: 2019-08-08 22:37:42Z
    Duration: 1.082 seconds

However, when I run both of them together, this happens:

D:\temp\Nunit.Test>nunit3-console.exe --noresult Test35\bin\Debug\Test35.dll Test40\bin\Debug\Test40.dll
NUnit Console Runner 3.10.0 (.NET 2.0)
Copyright (c) 2019 Charlie Poole, Rob Prouse
Freitag, 9. August 2019 00:42:16

Runtime Environment
   OS Version: Microsoft Windows NT 10.0.18362.0
  CLR Version: 4.0.30319.42000

Test Files
    Test35\bin\Debug\Test35.dll
    Test40\bin\Debug\Test40.dll


Errors, Failures and Warnings

1) Failed : Test35.TestFor35.Example
  Expected: <2.0.0.0>
  But was:  <4.0.0.0>
   bei Test35.TestFor35.Example() in D:\temp\Nunit.Test\Test35\TestFor35.cs:Zeile 12.

Run Settings
    DisposeRunners: True
    WorkDirectory: D:\temp\Nunit.Test
    ImageRuntimeVersion: 2.0.50727
    ImageRequiresX86: False
    ImageRequiresDefaultAppDomainAssemblyResolver: False
    NumberOfTestWorkers: 4

Test Run Summary
  Overall result: Failed
  Test Count: 2, Passed: 1, Failed: 1, Warnings: 0, Inconclusive: 0, Skipped: 0
    Failed Tests - Failures: 1, Errors: 0, Invalid: 0
  Start time: 2019-08-08 22:42:16Z
    End time: 2019-08-08 22:42:17Z
    Duration: 1.426 seconds

Interestingly, when I run them with --domain=Multiple (which should be the default according to the docs) this happens:

D:\temp\Nunit.Test>nunit3-console.exe --domain=Multiple --noresult Test35\bin\Debug\Test35.dll Test40\bin\Debug\Test40.dll
NUnit Console Runner 3.10.0 (.NET 2.0)
Copyright (c) 2019 Charlie Poole, Rob Prouse
Freitag, 9. August 2019 00:47:15

Runtime Environment
   OS Version: Microsoft Windows NT 10.0.18362.0
  CLR Version: 4.0.30319.42000

Test Files
    Test35\bin\Debug\Test35.dll
    Test40\bin\Debug\Test40.dll


Test Run Summary
  Overall result: Unknown
  Test Count: 0, Passed: 0, Failed: 0, Warnings: 0, Inconclusive: 0, Skipped: 0
  Start time: 2019-08-08 22:47:16Z
    End time: 2019-08-08 22:47:16Z
    Duration: 0.477 seconds

[PoByBolek]

Here’s the sample repository: https://github.com/PoByBolek/Nunit.Test

[ChrisMaddock]

Fixed by #670