title: Pytest: pass one fixture to another
body: <p>Is it possible to pass one fixture object to another in <a href="https://docs.pytest.org/en/2.8.7/fixture.html" rel="noreferrer">Pytest</a>? For example, suppose I want to have two fixture objects: one that's a numpy array, and another that's some model of that array:</p>
  
  <pre><code>import pytest
  import numpy as np
  
  @pytest.fixture()
  def arr():
    np.random.seed(141)
    return np.random.seed(141)
  
  @pytest.fixture()
  def model(arr):
    return arr * 2
  
  def test_multiplication(arr, model):
    assert model == arr * 2
  </code></pre>
  
  <p>Here <code>arr</code> is type <code>function</code> but <code>arr()</code> is <code>NoneType</code> inside model, which confuseth me.</p>
  
  <p>The use case for this is a case where some tests need access to the raw <code>arr</code> itself, while others need access to the models.</p>
  
  <p>To make this work, however, one needs to pass one fixture to another (so we can build the model using the array). Is this possible? Any help others can offer would be greatly appreciated!</p>