title: Pytest Fails with AssertionError False is False
body: <p>Since one day I am faceing a rally strange error when running my pytests, they fail with either</p>
  <pre><code>E    assert False is False
  AssertionError
  </code></pre>
  <pre><code>E    assert True is True
  AssertionError
  </code></pre>
  <p>But from my understanding and when checking it in python terminal that should give the correct output:</p>
  <pre class="lang-py prettyprint-override"><code>Python 3.6.9 (default, Oct  8 2020, 12:12:24) 
  &gt;&gt;&gt; False is False
  True
  </code></pre>
  <p>The outputs from pytest before running it</p>
  <pre><code>platform linux -- Python 3.6.8, pytest-6.2.2, py-1.10.0, pluggy-0.13.1
  plugins: cov-2.11.1, instafail-0.4.2, timeout-1.4.2
  </code></pre>
  <p>Does anyone have an idea what causes this behavior, because for me it makes no sense at all?</p>
  <h2>Important info</h2>
  <p>My question is not about the test itself it is about how can it happen, that pytest raises an explicit error telling me False is False is not True but False == False works without a problem?</p>
  <p>This actually reproduces the issue:</p>
  <pre><code>from typing import Tuple
  import numpy as np
  import pytest
  
  class MyObject():
      def function_to_text(self, input: list) -&gt; Tuple[bool, float]:
          val = np.array(0) &gt; 10
          return val, 1.0
  
  
  @pytest.fixture(scope='session')
  def my_object():
      my_obj = MyObject()
      yield my_obj
  
  
  def test_function_rejects_input(my_object):
  
      assert my_object.function_to_text([])[0] is False
  
  </code></pre>
  <p>And by finding a way to reproduce this one now, I know now also what is the problem, see the  answer for the solution</p>