Add .NET7 as a build target for the test suite

[stevenaw]

.NET7 will be coming out in ~2 months. Once CI supports it, it would be good to add it as a test target to ensure the framework runs as expected on that runtime.

[KonH]

I started to dig into this issue, current results in the draft PR above:

• .NET SDK 7.0 RC is used, and should be changed when a stable version is released
• Build is finished successfully
• Found one test which fails on "TestNetFramework on net7.0" but not on "TestNetFramework on net6.0" - https://github.com/nunit/nunit/blob/master/src/NUnitFramework/tests/Assertions/WarningTests.cs#L226
  No changes made on the CI side yet, will do it later

[KonH]

Considering CI:

• GitHub action now could run but require approval
• AppVeyor doesn't have VS 2022 preview support - https://www.appveyor.com/docs/windows-images-software/#visual-studio-2022, build fails (potentially it can be resolved via additional build steps, but I'm not sure that it worth it now)
• Azure Pipelines - build fails because of the new fail test described above

[KonH]

Considering test (https://github.com/nunit/nunit/blob/master/src/NUnitFramework/tests/Assertions/WarningTests.cs#L226) failure:
I found that stacktraces are different like this:
.NET 6.0:

at NUnit.TestData.WarningFixture.<>c__DisplayClass95_0.<WarningInThreadPoolQueueUserWorkItem>b__0(Object _) in F:\KonH\Work\Git\nunit\src\NUnitFramework\testdata\WarningFixture.cs:line 665
   at System.Threading.QueueUserWorkItemCallback.<>c.<.cctor>b__6_0(QueueUserWorkItemCallback quwi)

.NET 7.0:

   at NUnit.TestData.WarningFixture.<>c__DisplayClass95_0.<WarningInThreadPoolQueueUserWorkItem>b__0(Object _) in F:\KonH\Work\Git\nunit\src\NUnitFramework\testdata\WarningFixture.cs:line 665
   at System.Threading.QueueUserWorkItemCallback.Execute()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading.PortableThreadPool.WorkerThread.WorkerThreadStart()

Will investigate it later.

[KonH]

Potentially it is related to dotnet/runtime#71719
Now I just use additional define to cover that case
I also found second .NET 7 failing test case - https://github.com/nunit/nunit/blob/master/src/NUnitFramework/nunitlite.tests/TextUIReportTests.cs#L111
It looks like a flaky one now

[KonH]

Considering https://github.com/nunit/nunit/blob/master/src/NUnitFramework/nunitlite.tests/TextUIReportTests.cs#L111 test:
.NET 6:

0: Errors, Failures and Warnings
1:
2: 1) Invalid : NUnit.Tests.Assemblies.MockTestFixture.NonPublicTest
3: Method is not public
4:
5: 2) Failed : NUnit.Tests.Assemblies.MockTestFixture.FailingTest
6: Intentional failure
7: at NUnit.Tests.Assemblies.MockTestFixture.FailingTest() in F:\KonH\Work\Git\nunit\src\NUnitFramework\mock-assembly\MockAssembly.cs:line 126
8:
9: 3) Warning : NUnit.Tests.Assemblies.MockTestFixture.WarningTest
10: Warning Message                                                                                                                                                                                                            11: at NUnit.Tests.Assemblies.MockTestFixture.WarningTest() in F:\KonH\Work\Git\nunit\src\NUnitFramework\mock-assembly\MockAssembly.cs:line 132
12:
13: 4) Invalid : NUnit.Tests.Assemblies.MockTestFixture.NotRunnableTest
14: No arguments were provided
15:
16: 5) Error : NUnit.Tests.Assemblies.MockTestFixture.TestWithException
17: System.Exception : Intentional Exception
18: at NUnit.Tests.Assemblies.MockTestFixture.MethodThrowsException() in F:\KonH\Work\Git\nunit\src\NUnitFramework\mock-assembly\MockAssembly.cs:line 178
19: at NUnit.Tests.Assemblies.MockTestFixture.TestWithException() in F:\KonH\Work\Git\nunit\src\NUnitFramework\mock-assembly\MockAssembly.cs:line 173
20:

.NET 7.0 run 1:

0: Errors, Failures and Warnings
1:
2: 1) Invalid : NUnit.Tests.Assemblies.MockTestFixture.NonPublicTest
3: Method is not public
4:
5: 2) Failed : NUnit.Tests.Assemblies.MockTestFixture.FailingTest
6: Intentional failure
7: at NUnit.Tests.Assemblies.MockTestFixture.FailingTest() in F:\KonH\Work\Git\nunit\src\NUnitFramework\mock-assembly\MockAssembly.cs:line 126
8: at InvokeStub_MockTestFixture.FailingTest(Object, Object, IntPtr*) <= new line
9:
10: 3) Warning : NUnit.Tests.Assemblies.MockTestFixture.WarningTest
11: Warning Message
12: at NUnit.Tests.Assemblies.MockTestFixture.WarningTest() in F:\KonH\Work\Git\nunit\src\NUnitFramework\mock-assembly\MockAssembly.cs:line 132
13: at InvokeStub_MockTestFixture.WarningTest(Object, Object, IntPtr*) <= new line
14:
15: 4) Invalid : NUnit.Tests.Assemblies.MockTestFixture.NotRunnableTest
16: No arguments were provided
17:
18: 5) Error : NUnit.Tests.Assemblies.MockTestFixture.TestWithException
19: System.Exception : Intentional Exception
20: at NUnit.Tests.Assemblies.MockTestFixture.MethodThrowsException() in F:\KonH\Work\Git\nunit\src\NUnitFramework\mock-assembly\MockAssembly.cs:line 178
21: at NUnit.Tests.Assemblies.MockTestFixture.TestWithException() in F:\KonH\Work\Git\nunit\src\NUnitFramework\mock-assembly\MockAssembly.cs:line 173
22: at InvokeStub_MockTestFixture.TestWithException(Object, Object, IntPtr*) <= new line
23: at System.Reflection.MethodInvoker.Invoke(Object obj, IntPtr* args, BindingFlags invokeAttr) <= new line
24:

.NET 7.0 run 2:

0: Errors, Failures and Warnings
1:
2: 1) Invalid : NUnit.Tests.Assemblies.MockTestFixture.NonPublicTest
3: Method is not public
4:
5: 2) Failed : NUnit.Tests.Assemblies.MockTestFixture.FailingTest
6: Intentional failure
7: at NUnit.Tests.Assemblies.MockTestFixture.FailingTest() in F:\KonH\Work\Git\nunit\src\NUnitFramework\mock-assembly\MockAssembly.cs:line 126
8: <= no new line compare to previous run (!)
9: 3) Warning : NUnit.Tests.Assemblies.MockTestFixture.WarningTest
10: Warning Message
11: at NUnit.Tests.Assemblies.MockTestFixture.WarningTest() in F:\KonH\Work\Git\nunit\src\NUnitFramework\mock-assembly\MockAssembly.cs:line 132
12: at InvokeStub_MockTestFixture.WarningTest(Object, Object, IntPtr*) <= new line
13:
14: 4) Invalid : NUnit.Tests.Assemblies.MockTestFixture.NotRunnableTest
15: No arguments were provided
16:
17: 5) Error : NUnit.Tests.Assemblies.MockTestFixture.TestWithException
18: System.Exception : Intentional Exception
19: at NUnit.Tests.Assemblies.MockTestFixture.MethodThrowsException() in F:\KonH\Work\Git\nunit\src\NUnitFramework\mock-assembly\MockAssembly.cs:line 178
20: at NUnit.Tests.Assemblies.MockTestFixture.TestWithException() in F:\KonH\Work\Git\nunit\src\NUnitFramework\mock-assembly\MockAssembly.cs:line 173
21: at InvokeStub_MockTestFixture.TestWithException(Object, Object, IntPtr*) <= new line
22: at System.Reflection.MethodInvoker.Invoke(Object obj, IntPtr* args, BindingFlags invokeAttr) <= new line
23:

It looks pretty strange now

[KonH]

I've added a simple workaround, and now 2/3 platforms passed the test suite successfully