I just had this come up. This was 'fun' to track down.

    public async Task<SomeType> GetSomethingAsync()
    {
        await Task.Delay(10); // just to get rid of the async method does not await anything warning for anybody testing this
        return null;
    }
    public void SomeOtherFunction()
    {
        if (GetSomethingAsync() == null)
            DoSomethingIfNotFound();
        else
            DoSomethingElse();
    }

No warning about an asynchronous call not being awaited awaited, unreachable code / redundant tests, or anything. It happily compiles and executes without warning or error. Reminds me a lot of an if( a = b ) bug in C++ if not even nastier. If you don't see the bug, the return type of GetSomethingAsync is a task, not a SomeType. But both can be compared to null. So this test will never get a null since GetSomethingAsync() willl always return a non-null Task who's Result may or may not be null, but always would be in this sample code. Consequently DoSomethingElse() is executed 100% of the time even though you'd expect DoSomethingIfNotFound to be executed 100% of the time. The fix is simply to convert SomeOtherFunction to an async method and await GetSomethingAsync() or change the test to GetSomethingAnsync().Result == null.

Now I'm paranoid I might have missed this elsewhere...