Remove dependency on plumbum

tests/util_test.py

@@ -0,0 +1,17 @@
+from __future__ import absolute_import
+from __future__ import unicode_literals
+
+import pytest
+
+from pre_commit_hooks.util import CalledProcessError
+from pre_commit_hooks.util import cmd_output
+
+
+def test_raises_on_error():
+    with pytest.raises(CalledProcessError):
+        cmd_output('sh', '-c', 'exit 1')
+
+
+def test_output():
+    ret = cmd_output('sh', '-c', 'echo hi')
+    assert ret == 'hi\n'