From f8df7e75ded8202f5cf8ca3e3b770c4c48352a22 Mon Sep 17 00:00:00 2001
From: Stephan Hoyer <shoyer@gmail.com>
Date: Fri, 28 Oct 2016 10:58:48 -0700
Subject: [PATCH] Better error checking and tests for xarray.set_options

---
 xarray/core/options.py      |  6 +++++-
 xarray/test/test_options.py | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 xarray/test/test_options.py

diff --git a/xarray/core/options.py b/xarray/core/options.py
index 0594a1ce36d..0a3493d63ed 100644
--- a/xarray/core/options.py
+++ b/xarray/core/options.py
@@ -2,7 +2,7 @@
 
 
 class set_options(object):
-    """Set global state within a controlled context
+    """Set options for xarray in a controlled context.
 
     Currently, the only supported option is ``display_width``, which has a
     default value of 80.
@@ -24,6 +24,10 @@ class set_options(object):
     >>> xr.set_options(display_width=80)
     """
     def __init__(self, **kwargs):
+        invalid_options = {k for k in kwargs if k not in OPTIONS}
+        if invalid_options:
+            raise ValueError('argument names %r are not in the set of valid '
+                             'options %r' % (invalid_options, set(OPTIONS)))
         self.old = OPTIONS.copy()
         OPTIONS.update(kwargs)
 
diff --git a/xarray/test/test_options.py b/xarray/test/test_options.py
new file mode 100644
index 00000000000..8eb9f541db7
--- /dev/null
+++ b/xarray/test/test_options.py
@@ -0,0 +1,19 @@
+import xarray
+import pytest
+
+from xarray.core.options import OPTIONS
+
+
+def test_invalid_option_raises():
+    with pytest.raises(ValueError):
+        xarray.set_options(not_a_valid_options=True)
+
+
+def test_nested_options():
+    original = OPTIONS['display_width']
+    with xarray.set_options(display_width=1):
+        assert OPTIONS['display_width'] == 1
+        with xarray.set_options(display_width=2):
+            assert OPTIONS['display_width'] == 2
+        assert OPTIONS['display_width'] == 1
+    assert OPTIONS['display_width'] == original