Replace a few outdated references to py.test with pytest (#6063)

Replace a few outdated references to py.test with pytest

testing/freeze/runtests_script.py

@@ -1,6 +1,6 @@
 """
 This is the script that is actually frozen into an executable: simply executes
-py.test main().
+pytest main().
 """
 
 if __name__ == "__main__":

testing/python/collect.py

@@ -1148,7 +1148,7 @@ def test_dont_collect_non_function_callable(testdir):
     """Test for issue https://github.com/pytest-dev/pytest/issues/331
 
     In this case an INTERNALERROR occurred trying to report the failure of
-    a test like this one because py test failed to get the source lines.
+    a test like this one because pytest failed to get the source lines.
     """
     testdir.makepyfile(
         """

testing/test_reports.py

@@ -133,17 +133,17 @@ class TestReportSerialization:
         """
         reprec = testdir.inline_runsource(
             """
-            import py
+            import pytest
             def test_pass(): pass
             def test_fail(): 0/0
-            @py.test.mark.skipif("True")
+            @pytest.mark.skipif("True")
             def test_skip(): pass
             def test_skip_imperative():
-                py.test.skip("hello")
+                pytest.skip("hello")
-            @py.test.mark.xfail("True")
+            @pytest.mark.xfail("True")
             def test_xfail(): 0/0
             def test_xfail_imperative():
-                py.test.xfail("hello")
+                pytest.xfail("hello")
         """
         )
         reports = reprec.getreports("pytest_runtest_logreport")