improve documentation

tests.py

@@ -26,12 +26,15 @@ def test_os_chdir(tmp_path):
 
 
 def test_run_method(tmp_path):
+    """Run tests for run method."""
+
     run = mod.run
 
     # test a command with options:
     assert run(["date", "+%Y-%m-%d"]).returncode == 0
     assert run("date +%Y-%m-%d", shell=True).returncode == 0
 
+    # tests interacting with the file system
     with mod.os_chdir(str(tmp_path)):
         # ensure single string command works
         assert run(("ls -l"), shell=True).returncode == 0