Issue #2478: Decimal(sqrt(0)) failed when the decimal context
was not explicitly supplied.
diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
index 5e53318..46d2dc7 100644
--- a/Lib/test/test_decimal.py
+++ b/Lib/test/test_decimal.py
@@ -1315,6 +1315,12 @@
         d = d1.max(d2)
         self.assertTrue(type(d) is Decimal)
 
+    def test_implicit_context(self):
+        # Check results when context given implicitly.  (Issue 2478)
+        c = getcontext()
+        self.assertEqual(str(Decimal(0).sqrt()),
+                         str(c.sqrt(Decimal(0))))
+
 
 class DecimalPythonAPItests(unittest.TestCase):