title: Make pytest require code coverage only on full test suite run
body: <p>I am using something like</p>
  
  <pre><code># .coveragerc
  fail_under = 100
  </code></pre>
  
  <p>and</p>
  
  <pre><code># pytest.ini
  [pytest]
  addopts = --cov=modname/ --cov-report=term-missing
  </code></pre>
  
  <p>to make it so that my test suite runs the coverage and fails if it isn't 100%.</p>
  
  <p>This works, but the problem is that if I run only a subset of the tests, like</p>
  
  <pre><code>pytest some/specific/test.py
  </code></pre>
  
  <p>it then complains that the coverage is not 100%, because of course that one single test file doesn't cover the entire codebase. Is there a better way to make pytest run coverage, but only when running the full test suite? </p>