Add some missing no cover comments

pre_commit/languages/pcre.py

@@ -16,7 +16,7 @@ def install_environment(repo_cmd_runner, version='default'):
 
 def run_hook(repo_cmd_runner, hook, file_args):
     grep_command = 'grep -H -n -P'
-    if platform == 'darwin':
+    if platform == 'darwin':  # pragma: no cover (osx)
         grep_command = 'ggrep -H -n -P'
 
     # For PCRE the entry is the regular expression to match

pre_commit/output.py

@@ -10,7 +10,7 @@ from pre_commit import five
 
 # TODO: smell: import side-effects
 try:
-    if not os.environ.get('TERM'):
+    if not os.environ.get('TERM'):  # pragma: no cover (dumb terminal)
         raise OSError('Cannot determine width without TERM')
     COLS = int(
         subprocess.Popen(

testing/resources/failing_hook_repo/bin/hook.sh

@@ -1,6 +1,4 @@
 #!/usr/bin/env bash
-
-
 echo 'Fail'
 echo $@
 exit 1