The InputTestFixture is designed to test low-level Input System functionality.

If you have tests that load scenes / create objects and otherwise affect global state you need to clean-up after each each test so that each tests can run in a clean environment,

Use a teardown method like the below to clean up any state left over by your tests. For the tests provided in this bug report the following will work.

public class Framework : InputTestFixture
{
private void Cleanup()
{
var activeScene = SceneManager.GetActiveScene();
foreach (var go in activeScene.GetRootGameObjects())
{
if (go.name.Contains("Protagonist"))
{
UnityEngine.Object.Destroy(go);

// We could just destroy the PlayerInput component:
//
// var pi = go.GetComponent<UnityEngine.InputSystem.PlayerInput>();
// if (pi != null) UnityEngine.Object.Destroy(pi);
}
}
}
[TearDown]
public override void TearDown()
{
Cleanup();
base.TearDown();
}
}