Unit tests incorrectly using ThrowsAsync<>

[fig-nwebb]

Many of the unit tests are using ThrowsAsync<> incorrectly, in the form of:

[Fact]
public void TestTheThing()
{
    proxyClient = new();
    _ = Assert.ThrowsAsync<ArgumentExpection>(async () => /* do something with the client */);
}

Unfortunately, failing to await the call to Assert.ThrowsAsync will cause the test harness to only check that something deriving from Exception came back, not the actual specified type. Relevant GH issue.

In addition to the above, fixing these tests will result in additional breaks, in some cases. Assert.ThrowsAsync will look for the exact type that was specified. If the test is looking for ArgumentExpection but the logic under test throws ArgumentNullException, the test will fail.