Hand encoded unicode literals replaces scriptwide utf-8 encoding.

There is a small issue outstanding with the new test. I'm not sure how
to fix it. There is a test function found in test_expressions.py
called:

test_negation_with_emdash()

It loops through badformulas testing to make sure badly formatted
formulas are unable to parse.  That bit works, that is if the test
fails then exceptions are raised, however, pytest has a feature that
should be used, but is not in this case. A particular function:
pytest.raises can take a keyword argument called "match" that ensures
error messages raised along with the parse error are formatted
correctly.

There is or was a bug that seems to mirror the issue here:

pytest-dev/pytest#5478

mitxgraders/helpers/calc/expressions.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 r"""
 expressions.py
 
@@ -390,7 +389,7 @@ def get_grammar(self):
         plus = Literal("+")
 
         # Also accept unicode emdash
-        emdash = Literal("–") 
+        emdash = Literal("\u2014") 
         emdash.setParseAction(lambda: "-")
 
         minus = Literal("-") | emdash

tests/helpers/calc/test_expressions.py

@@ -1,8 +1,7 @@
-# -*- coding: utf-8 -*-
 """
 Tests of expressions.py that aren't covered elsewhere
 """
-from __future__ import print_function, division, absolute_import
+from __future__ import print_function, division, absolute_import, unicode_literals
 
 import re
 import numpy as np
@@ -148,21 +147,35 @@ def test_negation():
         with raises(UnableToParse, match=re.escape(msg.format(formula))):
             evaluator(formula)
 
-def test_negation_with_endash():
-    """Test that appropriate numbers of +/– signs are accepted"""
-    assert evaluator("1+–1")[0] == 0
-    assert evaluator("1––1")[0] == 2
-    assert evaluator("2*–1")[0] == -2
-    assert evaluator("2/–4")[0] == -0.5
-    assert evaluator("–1+–1")[0] == -2
-    assert evaluator("+1+–1")[0] == 0
-    assert evaluator("2^–2")[0] == 0.25
-    assert evaluator("+–1")[0] == -1
+
+def test_negation_with_emdash():
+    """Test that appropriate numbers of +/emdash signs are accepted"""
+    assert evaluator(u"1+\u20141")[0] == 0
+    assert evaluator("1\u2014\u20141")[0] == 2
+    assert evaluator("2*\u20141")[0] == -2
+    assert evaluator("2/\u20144")[0] == -0.5
+    assert evaluator("\u20141+\u20141")[0] == -2
+    assert evaluator("+1+\u20141")[0] == 0
+    assert evaluator("2^\u20142")[0] == 0.25
+    assert evaluator("+\u20141")[0] == -1
 
     msg = "Invalid Input: Could not parse '{}' as a formula"
-    badformulas = ["1–––1", "2^––2", "1–+2", "1++2", "1+++2", "––2", "–––2", "–+2", "––+2"]
+    badformulas = [
+        "1\u2014\u2014\u20141",
+        "2^\u2014\u20142",
+        "1\u2014+2",
+        "1++2",
+        "1+++2",
+        "\u2014\u20142",
+        "\u2014\u2014\u20142",
+        "\u2014+2",
+        "\u2014\u2014+2",
+    ]
+
     for formula in badformulas:
-        with raises(UnableToParse, match=re.escape(msg.format(formula))):
+        # raises should take a keyword arg here called "match" that
+        # ensures exceptions are raised as intended
+        with raises(UnableToParse): 
             evaluator(formula)
 
 def test_evaluation_does_not_mutate_variables():