Update pytest infrastructure, add pytest-cov package (#250)

Since travis isn't used as of #245 this isn't a travis thing.

Author: tony

Pipfile

@@ -14,6 +14,7 @@ libtmux = {path = ".",editable = true}
 black = "==19.3b0"
 sphinx-issues = "*"
 pytest-cov = "*"
+coverage = "*"
 
 [packages]
 

Pipfile.lock

@@ -1 +1,3 @@
-pytest==4.5.0
+pytest<6
+pytest-cov
+coverage

requirements/test.txt

@@ -9,7 +9,6 @@
 import sys
 
 from setuptools import setup
-from setuptools.command.test import test as TestCommand
 
 about = {}
 with open("libtmux/__about__.py") as fp:
@@ -26,20 +25,6 @@
 history = open('CHANGES').read().replace('.. :changelog:', '')
 
 
-class PyTest(TestCommand):
-    user_options = [('pytest-args=', 'a', "Arguments to pass to py.test")]
-
-    def initialize_options(self):
-        TestCommand.initialize_options(self)
-        self.pytest_args = []
-
-    def run_tests(self):
-        import pytest
-
-        errno = pytest.main(self.pytest_args)
-        sys.exit(errno)
-
-
 setup(
     name=about['__title__'],
     version=about['__version__'],
@@ -58,7 +43,6 @@ def run_tests(self):
     packages=['libtmux'],
     include_package_data=True,
     tests_require=tests_reqs,
-    cmdclass={'test': PyTest},
     zip_safe=False,
     keywords=about['__title__'],
     classifiers=[