pytest: New component

Pytest is used to test wendelin.core, zodbtools and pygolang
It is also used in component/unstable/pyodide, but currently via pip.

component/pytest/buildout.cfg

+# SlapOS component for pytest.
+# https://pytest.org
+
+[buildout]
+parts = pytest/scripts
+
+[pytest]
+recipe  = zc.recipe.egg:eggs
+eggs    = pytest
+
+[pytest/scripts]
+recipe  = zc.recipe.egg:scripts
+eggs    = ${pytest:eggs}
+
+
+[versions]
+pytest  = 4.6.11
+py      = 1.9.0
+pluggy  = 0.13.1
+
+pathlib2= 2.3.5
+scandir = 1.10.0
+
+wcwidth = 0.2.5
+backports.functools-lru-cache = 1.6.1
+
+more-itertools = 5.0.0
+atomicwrites = 1.4.0
+funcsigs = 1.0.2
+
+importlib-metadata = 1.7.0
+zipp = 1.2.0
+contextlib2 = 0.6.0.post1
+configparser = 4.0.2