C# 8 introduces default interface method implementations. Attempt to mock such methods with JustMock in elevated mode fails. The following example illustrates the issue:

public interface IMyInterface
{
    int IntProperty { get => 0; }
}


[TestClass]
public class UnitTest1
{
    [TestMethod]
    public void TestMethod1()
    {
        var mock = Mock.Create<IMyInterface>();
        Mock.Arrange(() => mock.IntProperty).Returns(1);

        Assert.AreEqual(1, mock.IntProperty);
    }
}

I've already created an issue in the JustMock repo, you can find it here: https://github.com/telerik/JustMockLite/issues/162. Below is the text from that issue...

I'm currently working on a PR to add JustMock to the suite of performance tests that currently exist in that repository. The problem is that some of the tests (like OneParameter and Callback) take a long time to finish for JustMock. I'm not sure why, but it's making it such that JustMock can't be added to the test suite. More to the point, the PR can't be accepted as-is because it would take too long to finish.

One thing Steve (owner of the repo) and I talked about is if the invocationCount value passed to the SimpleJobAttribute (which exists on both the MockingBenchmark and MockingBenchmark<T> classes) is reduced from 100,000 to something like 1,000, the tests then finish, but that doesn't address the underlying issue why these tests for JustMock slow down over repeated called.

There may be something in the benchmark tests with the way I've set things up with JustMock that may be incorrect. I've never used JustMock until today :). If there's something that I'm doing right, please let me know.

I filed a prior ThreadLeak:

Thread leak in JustMock (telerik.com)

I think I've found another one: (VS version 16.10.31321.278)

telerik_justmock_debugwindow_service_client!Telerik.JustMock.DebugWindow.Service.Client.ServiceHostMonitor.MonitorTimer_Elapsed

Apparently, the MonitorTimer_Elapsed code is running on a threadpool thread and it takes longer than 1 sec (perhaps it's waiting on a lock?).

Another timer tick occurs and the method is called again. Eventually, the ThreadPool runs out of threads and grows by about 1 thread per second (1Mb /sec leak)

In one dump 2Gig was used (1962 threads on the same MonitorTimer_Elapsed stack frame)

In that same dump there were 52 stacks with this frame:

telerik_justmock_debugwindow_service_client!Telerik.JustMock.DebugWindow.Service.Client.ConnectionSetupServiceClientBase`[[System.__Canon,mscorlib]].get_ServiceAvailable

(this was the same item as my prior report).

The following test fails:

[TestMethod]
public void TestCallOrderWithInOrder()
{
	// Arrange
	var mockClass1 = Mock.Create<Class1>();
	var mockClass2 = Mock.Create<Class2>();

	Mock.Arrange(() => mockClass1.Method1())
		.InOrder();
	Mock.Arrange(() => mockClass2.Method1())
		.InOrder()
		.Occurs(2);
	Mock.Arrange(() => mockClass1.Method2())
		.InOrder();

	// Act
	mockClass1.Method1();

	mockClass2.Method1();
	mockClass2.Method1(); // <--- this call is not allowed by
						  //      InOrder clause currently 
						  //      and throws AssertFailedException

	mockClass1.Method2();

	// Assert
	Mock.Assert(mockClass1);
	Mock.Assert(mockClass2);
}

The following test is not working anymore since version JustMock_2021_2_615_4 but was working with JustMock_2021_1_326_1 and older versions:

public interface ITest
{
    void Test(string text);
}

[TestMethod]
public void MyTestMethod()
{
    var mock = Mock.Create<ITest>();
    Mock.Arrange(() => mock.Test("")).IgnoreArguments().OccursNever();
    Mock.Arrange(() => mock.Test(Arg.Matches<string>(a => a == "a"))).InOrder().OccursOnce();
    Mock.Arrange(() => mock.Test(Arg.Matches<string>(a => a == "b"))).InOrder().OccursOnce();


    mock.Test("a");
    mock.Test("b");

    Mock.Assert(mock);
}

If I remove the OccorsNever line, its working.
If I remove the 2 InOrder, its working.

Seems that something change there: https://www.telerik.com/support/whats-new/justmock/release-history/justmock-r2-sp1-2021

Currently, when the JustMock profiler is enabled it provides a performance hit on the test execution. This effect is expected because a profiler is involved.

What we can do is find a more optimized way of instrumenting the methods.

Allow the developer to create custom behaviors and use them in an arrangement. Something like the following:

            Mock.Arrange(() => foo.CalcData(Arg.AnyInt, Arg.AnyInt), new IBehavior[]
            {
                new LogInvocation(),
                new ReturnBaseOrDefaultValue(),
            });

The new public API should allow the developer to access the invocations for a particular arrangement. Something like the following:

IEnumerable<IInvocaiton> invocations = foo.GetInvocationsFor((x) => x.CalcData(2, 2));

Implement a new public API that will allow the developer to iterate over all invocations of mock arrangements. Something like the following:

IEnumerable<IInvocaiton> invocations = Mock.Invocations;

Using elevated mocking mode (profiler enabled) with long path names for the test containers (above 260 characters) causes the following command:

dotnet test

to fail with error:

Testhost process exited with error: Fatal error. System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
   at Microsoft.VisualStudio.TestPlatform.TestHost.Program.Main(System.String[])
. Please check the diagnostic logs for more information.

Test Run Aborted.

The documentation on Fluent Mocking ends with this statement:

Important

Note that when you use Fluent Asserts only arrangements marked with either MustBeCalled or Occurs will be verified. For other tests you have to use the explicit assert.

What this fails to note is that, while this is true of the function "Assert", there is another function, "AssertAll", which will flag an error if any Arranged function call was not utilized.

On a related note, I left other suggestions for this same page a day or two ago.  I would have liked to leave the above statement using the same feedback utility, but I can no longer find the control that I used to leave those initial suggestions.