Add color utility.

tests/color_test.py

@@ -0,0 +1,35 @@
+
+import mock
+import pytest
+import sys
+
+from pre_commit.color import format_color
+from pre_commit.color import GREEN
+from pre_commit.color import use_color
+
+
+@pytest.mark.parametrize(('in_text', 'in_color', 'in_use_color', 'expected'), (
+    ('foo', GREEN, True, '{0}foo\033[0m'.format(GREEN)),
+    ('foo', GREEN, False, 'foo'),
+))
+def test_format_color(in_text, in_color, in_use_color, expected):
+    ret = format_color(in_text, in_color, in_use_color)
+    assert ret == expected
+
+
+def test_use_color_never():
+    assert use_color('never') is False
+
+
+def test_use_color_always():
+    assert use_color('always') is True
+
+
+def test_use_color_no_tty():
+    with mock.patch.object(sys.stdout, 'isatty', return_value=False):
+        assert use_color('auto') is False
+
+
+def test_use_color_tty():
+    with mock.patch.object(sys.stdout, 'isatty', return_value=True):
+        assert use_color('auto') is True