NetworkList<T>.Contains(T) return value is inverted

[DapperDino]

Describe the bug
When calling NetworkList<T>.Contains(T) it is returning the opposite bool of what I'm expecting.

To Reproduce
Steps to reproduce the behavior:

1. Add an element to a NetworkList
2. Debug.Log the return value from: NetworkList<T>.Contains(T) passing in the element you added
3. Debug.Log the return value from: NetworkList<T>.Contains(T) passing in an element you didn't add
4. See log output

Actual outcome
False
True

Expected outcome
True
False

Screenshots
Looking at the source, it is returning true if the index of the element is -1, otherwise false. I'm pretty sure this is the cause of the issue.

public bool Contains(T item)
{
    int index = NativeArrayExtensions.IndexOf(m_List, item);
    return index == -1;
}

Environment (please complete the following information):

• OS: [Windows 10]
• Unity Version: [2021.1]
• Netcode Version: [v1.0.0-pre.2]

[0xFA11]

Looks like this bug introduced by PR #1149
It also shows that we don't have proper tests for NetworkList.
A quick fix with some unit tests would be ideal.
I have a tendency to leave this issue for @mattwalsh-unity but I might also take it when we triage, I just happened to be here earlier :)

[mattwalsh-unity]

It turns out we have a test but there was a typo...