touch up test_cmdline_python_namespace_package() test code

testing/acceptance_test.py

@@ -624,10 +624,9 @@ class TestInvocationVariants(object):
         for p in search_path:
             monkeypatch.syspath_prepend(p)
 
-        os.chdir('world')
         # mixed module and filenames:
+        os.chdir('world')
         result = testdir.runpytest("--pyargs", "-v", "ns_pkg.hello", "ns_pkg/world")
-        testdir.chdir()
         assert result.ret == 0
         result.stdout.fnmatch_lines([
             "*test_hello.py::test_hello*PASSED*",
@@ -638,6 +637,7 @@ class TestInvocationVariants(object):
         ])
 
         # specify tests within a module
+        testdir.chdir()
         result = testdir.runpytest("--pyargs", "-v", "ns_pkg.world.test_world::test_other")
         assert result.ret == 0
         result.stdout.fnmatch_lines([