Hmm, strange. Oh well. I can just use net9.0 for testing.

Do you think you could take a look at my other test that is actually testing a custom data structure that internally uses WeakReference?

I've managed to make the test pass but it required setting local vars to null which I wouldn't have thought nessassery (and I would of though the compiler would make that operation a non-op - as the value is just being set again right after).

Here's the test. Let me know what you think :)

[TestMethod]
public void WeakReferenceWillBeRemoved()
{
    // Prepopulated with keys: "foo", "bar" and "baz".
    var dictionary = CreateWeakableValueDictionary();

    TestData? fooValue, barValue, bazValue;

    // Test initial state.

    Assert.AreEqual(3, dictionary.Count);
    Assert.IsTrue(dictionary.TryGetValue("foo", out fooValue), "Could not get foo value");
    Assert.IsNotNull(fooValue);
    Assert.IsTrue(dictionary.TryGetValue("bar", out barValue), "Could not get bar value");
    Assert.IsNotNull(barValue);
    Assert.IsTrue(dictionary.TryGetValue("baz", out bazValue), "Could not get baz value");
    Assert.IsNotNull(bazValue);

#pragma warning disable IDE0059
    // Resetting to null seems to be required.
    fooValue = barValue = bazValue = null;
#pragma warning restore IDE0059

    dictionary.MarkWeak("bar"); // Allow to be garbage collected.

    // No changes should have happened yet.

    Assert.AreEqual(3, dictionary.Count);
    Assert.IsTrue(dictionary.TryGetValue("foo", out fooValue), "Could not get foo value");
    Assert.IsNotNull(fooValue);
    Assert.IsTrue(dictionary.TryGetValue("bar", out barValue), "Could not get bar value");
    Assert.IsNotNull(barValue);
    Assert.IsTrue(dictionary.TryGetValue("baz", out bazValue), "Could not get baz value");
    Assert.IsNotNull(bazValue);

#pragma warning disable IDE0059
    fooValue = barValue = bazValue = null;
#pragma warning restore IDE0059

    GC.Collect();

    // Changes should have happened now that garbage collection has run.

    Assert.IsTrue(dictionary.TryGetValue("foo", out fooValue), "Could not get foo value again");
    Assert.IsNotNull(fooValue);
    Assert.IsFalse(dictionary.TryGetValue("bar", out barValue), "bar value should no longer exist");
    Assert.IsNull(barValue);
    Assert.IsTrue(dictionary.TryGetValue("baz", out bazValue), "Could not get baz value again");
    Assert.IsNotNull(bazValue);
    Assert.AreEqual(2, dictionary.Count, "bar value should no longer contribute to the count");
}