Add check_path hook

Adds a hook which can be used for preventing commits to paths specified
by regex.

tests/check_path_edits_test.py

@@ -0,0 +1,45 @@
+from pre_commit_hooks.check_path_edits import find_wrong_paths
+from pre_commit_hooks.check_path_edits import main
+from pre_commit_hooks.util import cmd_output
+
+
+def test_nothing_added(temp_git_dir):
+    with temp_git_dir.as_cwd():
+        assert find_wrong_paths(['f.py'], {'asd'}) == 0
+
+
+def test_adding_something(temp_git_dir):
+    with temp_git_dir.as_cwd():
+        temp_git_dir.join('f.py').write("print('hello world')")
+        cmd_output('git', 'add', 'f.py')
+
+        assert find_wrong_paths(['f.py'], {'^f.*'}) == 1
+
+
+def test_some_regex(temp_git_dir):
+    with temp_git_dir.as_cwd():
+        temp_git_dir.join('f.py').write('a' * 10000)
+
+        # Should not fail when not added
+        assert find_wrong_paths(['f.py'], {'.*'}) == 0
+
+        cmd_output('git', 'add', 'f.py')
+
+        assert find_wrong_paths(['f.py'], {'.*'}) == 1
+
+        assert find_wrong_paths(['f.py'], {'dasd', 'py', 'asd'}) == 1
+
+        assert find_wrong_paths(['f.py'], {'^py'}) == 0
+
+
+def test_integration(temp_git_dir):
+    with temp_git_dir.as_cwd():
+        assert main(argv=[]) == 0
+
+        temp_git_dir.join('f.py').write('a')
+        cmd_output('git', 'add', 'f.py')
+
+        # Should not fail with default
+        assert main(argv=['f.py']) == 0
+
+        assert main(argv=['--pattern', 'f.py', 'f.py']) == 1