Add pre-commit try-repo

`try-repo` is useful for:
- Trying out a remote hook repository without needing to configure it.
- Testing a hook repository while developing it.

tests/commands/try_repo_test.py

@@ -0,0 +1,71 @@
+from __future__ import absolute_import
+from __future__ import unicode_literals
+
+import re
+
+from pre_commit.commands.try_repo import try_repo
+from pre_commit.util import cmd_output
+from pre_commit.util import cwd
+from testing.auto_namedtuple import auto_namedtuple
+from testing.fixtures import git_dir
+from testing.fixtures import make_repo
+from testing.util import run_opts
+
+
+def try_repo_opts(repo, ref=None, **kwargs):
+    return auto_namedtuple(repo=repo, ref=ref, **run_opts(**kwargs)._asdict())
+
+
+def _get_out(cap_out):
+    out = cap_out.get().replace('\r\n', '\n')
+    out = re.sub('\[INFO\].+\n', '', out)
+    start, using_config, config, rest = out.split('=' * 79 + '\n')
+    assert start == ''
+    assert using_config == 'Using config:\n'
+    return config, rest
+
+
+def _run_try_repo(tempdir_factory, **kwargs):
+    repo = make_repo(tempdir_factory, 'modified_file_returns_zero_repo')
+    with cwd(git_dir(tempdir_factory)):
+        open('test-file', 'a').close()
+        cmd_output('git', 'add', '.')
+        assert not try_repo(try_repo_opts(repo, **kwargs))
+
+
+def test_try_repo_repo_only(cap_out, tempdir_factory):
+    _run_try_repo(tempdir_factory, verbose=True)
+    config, rest = _get_out(cap_out)
+    assert re.match(
+        '^repos:\n'
+        '-   repo: .+\n'
+        '    sha: .+\n'
+        '    hooks:\n'
+        '    -   id: bash_hook\n'
+        '    -   id: bash_hook2\n'
+        '    -   id: bash_hook3\n$',
+        config,
+    )
+    assert rest == (
+        '[bash_hook] Bash hook................................(no files to check)Skipped\n'  # noqa
+        '[bash_hook2] Bash hook...................................................Passed\n'  # noqa
+        'hookid: bash_hook2\n'
+        '\n'
+        'test-file\n'
+        '\n'
+        '[bash_hook3] Bash hook...............................(no files to check)Skipped\n'  # noqa
+    )
+
+
+def test_try_repo_with_specific_hook(cap_out, tempdir_factory):
+    _run_try_repo(tempdir_factory, hook='bash_hook', verbose=True)
+    config, rest = _get_out(cap_out)
+    assert re.match(
+        '^repos:\n'
+        '-   repo: .+\n'
+        '    sha: .+\n'
+        '    hooks:\n'
+        '    -   id: bash_hook\n$',
+        config,
+    )
+    assert rest == '[bash_hook] Bash hook................................(no files to check)Skipped\n'  # noqa