Fail gracefully on undecodable install output.

tests/commands/run_test.py

@@ -371,6 +371,33 @@ def test_stdout_write_bug_py26(
         assert 'UnicodeDecodeError' not in stdout
 
 
+def test_hook_install_failure(mock_out_store_directory, tempdir_factory):
+    git_path = make_consuming_repo(tempdir_factory, 'not_installable_repo')
+    with cwd(git_path):
+        install(Runner(git_path))
+
+        # Don't want to write to home directory
+        env = dict(os.environ, PRE_COMMIT_HOME=tempdir_factory.get())
+        _, stdout, _ = cmd_output(
+            'git', 'commit', '-m', 'Commit!',
+            # git commit puts pre-commit to stderr
+            stderr=subprocess.STDOUT,
+            env=env,
+            retcode=None,
+            encoding=None,
+        )
+        assert b'UnicodeDecodeError' not in stdout
+        # Doesn't actually happen, but a reasonable assertion
+        assert b'UnicodeEncodeError' not in stdout
+
+        # Sanity check our output
+        assert (
+            b'An unexpected error has occurred: CalledProcessError: ' in
+            stdout
+        )
+        assert '☃'.encode('UTF-8') + '²'.encode('latin1') in stdout
+
+
 def test_get_changed_files():
     files = get_changed_files(
         '78c682a1d13ba20e7cb735313b9314a74365cd3a',

tests/error_handler_test.py

@@ -11,6 +11,7 @@ import mock
 import pytest
 
 from pre_commit import error_handler
+from pre_commit import five
 from pre_commit.errors import FatalError
 from pre_commit.util import cmd_output
 
@@ -82,7 +83,9 @@ def test_log_and_exit(mock_out_store_directory):
             write_fn=mocked_write,
         )
 
-    printed = ''.join(call[0][0] for call in mocked_write.call_args_list)
+    printed = ''.join(
+        five.to_text(call[0][0]) for call in mocked_write.call_args_list
+    )
     assert printed == (
         'msg: FatalError: hai\n'
         'Check the log at ~/.pre-commit/pre-commit.log\n'