pin pytest

tox.ini

@@ -11,10 +11,17 @@ requires =
     setuptools >= 30.3.0
     pip >= 19.3.1
     setuptools_scm
+    tox-pypi-filter >= 0.12
 isolated_build = true
 
 [testenv]
 
+# The following option combined with the use of the tox-pypi-filter above allows
+# project-wide pinning of dependencies, e.g. if new versions of pytest do not
+# work correctly with pytest-astropy plugins. Most of the time the pinnings file
+# should be empty.
+pypi_filter = https://raw.githubusercontent.com/astropy/ci-helpers/master/pip_pinnings.txt
+
 # Pass through the following environment variables which may be needed for the CI
 passenv = HOME WINDIR LC_ALL LC_CTYPE CC CI TRAVIS